Often times, after bms, i feel very weak and nauseous. i need to lie down for a little while to regain strength. usually loose stools. is this normal?

Things to consider--: Be very concerned if your weakness is relatively acute ;/or associated with fever, vomiting, bleeding, weight loss. Chronic symptoms without alarm signs deserve evaluation as well, particularly if accompanied by underlying pathology (diabetes, thyroid or adrenal problems, endocrinopathy, inflammatory, autoimmune, etc). Treatment depends on cause so please see a gastroenterologist for evaluation.