The tips of my index and thumb fingers of both hands feel swollen and a bit numb, but they visually seem fine. It comes and goes. What could it be?

Continue to monitor. Numbness and tingling in any extremity can be due to many reasons including sitting or standing in the same position for a long time, nerve injury, electrolyte abnormalities, vitamin deficiencies, etc. See your physician for evaluation if your symptoms persist or you develop new associated symptoms. http://www.ninds.nih.gov/disorders/paresthesia/paresthesia.htm.