If your weekends do not consist of a normal exercise routine, the gym may seem very daunting on Mondays. For various reasons I failed to exercise last weekend, but I was determined to get back on track on Monday.
The problem was that the idea of spending a full hour at the gym seemed like a horrible idea after taking three days off. So instead of pushing myself to do it, I just had a light cardio day. Nothing crazy, pretty easy, but still got me moving. Come Tuesday, I was back in the swing of things. Had I have pushed myself too hard on Monday then I may not have even made it to the gym on Tuesday and my whole routine would have been screwed up. So if you find that you're not exercising on the weekends and having a hard time getting back into it on Mondays, make yourself do something, just go easy. It will make the transition from the weekend into your full blown workout schedule a lot easier.