user5256: Sometimes I feel that my consciousness is separate from my body. How can this be explained in Buddhism? What is this state ? Can consciousness exist externally without physical body? 

user295: 
Can consciousness exist externally without physical body?

In The Immaterial World this is possible. There might be times you fee so in meditation. Maybe when you enter Infinite Conciousness Absorption but even without this there maybe instances you may fee so.

What is this state ?

You been born in an Immaterial World.

How can this be explained in Buddhism?

You have generally have Nama & Rupa. In Immaterial World you just have Nama but not Rupa.

Sometimes I feel that my consciousness is separate from my body.

This is not possible as I would believe you to be human hence having Nama and Rupa, in which case conciousness cannot exit without a physical body. This is the case in any other plane of existance other than The Immaterial Worlds.

user-1: 
Can consciousness exist externally without physical body?

Mind can exist without the physical body, i.e. Nama can exist without Rupa. Mind is not dependent on a physical body, whereas the physical body is fully dependent on Mind and cannot exist without it. The physical body cannot do anything before an intention arises in the Mind.
Some beings in other realms are "mind-only". They have no physical body and therefore no locality, hence they cannot be located in space. Since they have no physical body and therefore no ear-faculty, they are not able to hear Dhamma teachings.
These beings can be found in the Immaterial Realm (Arupa Loka).

What is this state?

One can gain access to the Immaterial Realm, e.g. through the Four Formless Jhanas.

How can this be explained in Buddhism?

The 31 Planes of Existence teaches about the different realms of existence and how to gain access to them.
The Abhidhamma teaches about Nama-Rupa.
The practice of Samatha Meditation will grant a being access to the Jhanas and thereby the different realms.
The practice of Vipassana Meditation will grant a being access to insights into how reality functions, e.g. the 3 marks of existence, how the Mind works, how the Mind-Body-Complex works, thereby beginning the process of purification of Mind by destroying the root defilements. 
The degree of purity of Mind corresponds to which realms a being can access/be reborn in. 

To add to my question, is my consciousness same as yours? Is it possible?

Yes, Consciousness is the same. Consciousness is not a thing, its a "knowing". One of the reasons this is not understandable intellectually, is because we use conventional language to talk about phenomena that cannot be reduced to conventional reality. 
The Buddha once said that it is okay to use conventional language but do not be fooled thereby.
Consciousness is the basic awareness of an object and nothing more. It only exists as a taker of objects. One will understand this when practicing Vipassana meditation. One will clearly see how there cannot be conscious experience without consciousness is present. 
Let me give you can example from daily life, which you might have experienced. You are reading a good book or watching a movie and then someone calls your name. You are absorped in the book or movie and therefore do not hear the person trying to get in contact with you. How is that? The sound from the other person is still there, yes?
That is because consciousness is not at the ear-sensebase at that moment. Consciousness is at the eye-sensebase. That is why you did not register the sound from the other person. The sound is still there but you are not aware of it, because consciousness did not take that object, at that particular time. 
One can only be aware of one object at a time. Mind can only arise to one object at a time. It might feel like one is aware of multiple objects at a time, but that is because Mind is shifting very rapidly and mindfulness is not strong enough to register that.

5256: <p>Sometimes I feel that my consciousness is separate from my body. How can this be explained in Buddhism? What is this state ? Can consciousness exist externally without physical body? </p>
 295: <blockquote>
  <p>Can consciousness exist externally without physical body?</p>
</blockquote>

<p>In <a href="http://www.accesstoinsight.org/ptf/dhamma/sagga/loka.html#arupa" rel="nofollow">The Immaterial World</a> this is possible. There might be times you fee so in meditation. Maybe when you enter Infinite Conciousness Absorption but even without this there maybe instances you may fee so.</p>

<blockquote>
  <p>What is this state ?</p>
</blockquote>

<p>You been born in an Immaterial World.</p>

<blockquote>
  <p>How can this be explained in Buddhism?</p>
</blockquote>

<p>You have generally have Nama &amp; Rupa. In Immaterial World you just have Nama but not Rupa.</p>

<blockquote>
  <p>Sometimes I feel that my consciousness is separate from my body.</p>
</blockquote>

<p>This is not possible as I would believe you to be human hence having Nama and Rupa, in which case conciousness cannot exit without a physical body. This is the case in any other plane of existance other than The Immaterial Worlds.</p>
 -1: <blockquote>
  <p>Can consciousness exist externally without physical body?</p>
</blockquote>

<p>Mind can exist without the physical body, i.e. Nama can exist without Rupa. Mind is not dependent on a physical body, whereas the physical body is fully dependent on Mind and cannot exist without it. The physical body cannot do anything before an <em>intention</em> arises in the Mind.</p>

<p>Some beings in other realms are "mind-only". They have no physical body and therefore no locality, hence they cannot be located in space. Since they have no physical body and therefore no <em>ear-faculty</em>, they are not able to hear Dhamma teachings.</p>

<p>These beings can be found in the <em>Immaterial Realm (Arupa Loka)</em>.</p>

<blockquote>
  <p>What is this state?</p>
</blockquote>

<p>One can gain access to the Immaterial Realm, e.g. through the <em>Four Formless Jhanas</em>.</p>

<blockquote>
  <p>How can this be explained in Buddhism?</p>
</blockquote>

<p><a href="http://www.accesstoinsight.org/ptf/dhamma/sagga/loka.html" rel="nofollow">The 31 Planes of Existence</a> teaches about the different realms of existence and how to gain access to them.</p>

<p>The Abhidhamma teaches about <em>Nama-Rupa</em>.</p>

<p>The practice of Samatha Meditation will grant a being access to the Jhanas and thereby the different realms.</p>

<p>The practice of Vipassana Meditation will grant a being access to insights into how reality functions, e.g. <em>the 3 marks of existence, how the Mind works, how the Mind-Body-Complex works</em>, thereby beginning the process of purification of Mind by destroying the root defilements. </p>

<p>The degree of purity of Mind corresponds to which realms a being can access/be reborn in. </p>

<blockquote>
  <p>To add to my question, is my consciousness same as yours? Is it possible?</p>
</blockquote>

<p>Yes, Consciousness is the same. Consciousness is not a thing, its a "knowing". One of the reasons this is not understandable intellectually, is because we use conventional language to talk about phenomena that cannot be reduced to conventional reality. </p>

<p>The Buddha once said that it is okay to use conventional language but do not be fooled thereby.</p>

<p>Consciousness is the basic awareness of an object and nothing more. It only exists as a taker of objects. One will understand this when practicing Vipassana meditation. One will clearly see how there cannot be conscious experience without consciousness is present. </p>

<p>Let me give you can example from daily life, which you might have experienced. You are reading a good book or watching a movie and then someone calls your name. You are absorped in the book or movie and therefore do not hear the person trying to get in contact with you. How is that? The sound from the other person is still there, yes?</p>

<p>That is because consciousness is not at the ear-sensebase at that moment. Consciousness is at the eye-sensebase. That is why you did not register the sound from the other person. The sound is still there but you are not aware of it, because consciousness did not take that object, at that particular time. </p>

<p>One can only be aware of one object at a time. Mind can only arise to one object at a time. It might feel like one is aware of multiple objects at a time, but that is because Mind is shifting very rapidly and mindfulness is not strong enough to register that.</p>
