Hi, periodic numbness is a common neurological phenomenon. Causes generally range from vascular compression, vascular insufficiency or incompetence, nerve compression or some electrolytes imbalance in the body. Calcium, Magnesium and Potassium blood levels are the most commonly implicated i term of electrolytes. In your case, the most likely cause shall be due to compression of particular blood vessels that supply nerves in given areas. This compression reduces blood supply to given nerves in that area and leading to decreased sensitivity in numbness. Another possibility, especially in the upper limbs, is compression given nerves especially when particular sleeping positions are adopted like the ulnar and radial nerve compressions. A clinical examinations with specific clinical manouvres are usually helpful in orienting diagnoses. Simple blood examination like measuring red blood cell sizes and shapes could give an orientation towards particular vitamin deficiency, calcium, potassium and magnesium blood levels could also be known. For mow, its advisable to avoid positions that cause these symptoms and visit a neurologist for a proper evaluation. Thanks and hope this helps, Luchuo, MD.