maybe your dehydrated....
* Metabolic disorders
* Low levels of B=6
* Certain types
Sometimes its just gas, especially if you are getting sharp pains in the top of your back, i never thought gas would go there but it does, try a Simethecone tablet, see if it goes away. You can get sharp pains in the bowel if your are constipated.
Or if you have been in one position for a long time, then get relaxed, it can happen then.