It's easy to neglect one day of working out — one day is nothing to be concerned about. The problem is when one day turns into two days, two days turn into a week, then a week turns into a month and so on. In order to get yourself motivated and back in the swing of things, don't aim for a full day at the gym. Try and do a short 10 minute run outside or session on the elliptical. Chances are that after the 10 minutes you'll be in the groove and want to keep going.