### instruction:
If you are a doctor, please answer the medical questions based on the patient's description.

### input:
HI there, I am at 36 year old woman who is physically fit and very healthy. I weigh 56kg and 172cm. For several years now I have had inappropriate sinus tachycardia. I run or exercise 5 days a week and usually my heart rate is around 160-180 on exercise. On resting first thing in the morning it I have felt it at 50 but never any lower than that. Early this week I felt sick and dizzy - I measured my h/r and it was 43. It went down to 39 but sat around 40-45 for a few hours and then came back to 60ish and the other sypmtoms disappeared. The same symptoms occured 2 days later while in the shower and again my h/r was 45. 2 days later again and I went to the bathroom. I felt dizzy while on the toilet (first thing in the AM). I went to get off and collapsed. My husband found me and after 1 minute was able to rouse me (I remember falling but no more). When the ambulance got here my b/p was 140/80 which is high for me (usually around 100/60 ish) and my heart rate was 43. I have the doctors stumped as my ECG only showed bradycardia. This morning the same dizzy symptoms and nausea occured while lying in bed. It was first thing in the morning and unusually my h/r was 75 then dropped suddenly to 45 within a minute. It was regular but did not stay low the entire time - instead fluctuating between the 40ish and 70ish mark. I am waiting for a halter monitor and will be seeing a cardiologist at some point but just wondered if you had any ideas? Thanks for your help!

### output:

Your low blood pressure has many causes, but let me focus on the most common :1- it may be idiopathic, as you say you are healthy and do exercise 5 days a week, many people complain of hypotension. If that, a fixed dose of ATP injections may strengthen your heart to achieve the suitable blood pressure, but you should first exclude any other cause .2- Aortic Stenosis, is narrowing in the aorta (the biggest vessel) which gives the blood to all your body tissues. An Echocardiogram is recommended to make sure, especially as you said (collapsed)3- Thyroid hypofunction (cretinism) , but it comes with weigh gain . And is diagnosed by a thyroid function test . (TSH, T3, T4)