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

### input:
Every few weeks (maybe 6/8 weeks) a strange thing happens to me which is baffling & worrying me.(as well as causing great pain)...It also happens when my body is under no strain/stress whatsoever. No heavy lifting is involved, I am not participating in any sport, I am not overeaching for anything, nor am I standing in some strange/unusual position....What happens to me is,...I get a totaly unexpected sudden severe pain at the bottom of my back, which I describe to friends as being like someone ramming a sword into the bottom of my spine from the back....As this happens, I fall to the floor, in a way that I can only describe as somebody switching my legs off . When I hit the floor, I know now from previous experiences, to try to lay flat on my back as soon as possible, which makes the hideous pain vanish in seconds. But whilst I try to adjust myself into the flat to the floor position, ALL movement however small, causes me pain equal to that which put me on the floor initialy....I am completely conscious throughout (this isn t some form of fainting )...and can have sensible conversation with anyone present, for the minute or so I stay on the floor, before being helped to my feet....When I am standing up again, there is no hint of pain, and I feel no sense of experiencing anything traumatic.?...I know myself, that it probably wont happen again for another few weeks, and so just carry on with the conversation (or whatever) I was having before it happened.....BUT I KNOW THERE IS SOMETHING NOT RIGHT.??...Can anyone suggest what may be causing this.? P.S. It only happens when in a standing posture.

### output:

Hi this may be due to orthostatic hypotension which occurs when you stand. And sudden pain in the back once in 6 or 8 weeks may be due to premenstrual symptoms. Will be better if you consult your physician and ask him to evaluate for you vitamin D levels calcium lave and have one bone scan done. If everything is normal take some medications prior to the expected date of your menstrual cycle to relieve your premenstrual symptoms.