I had the same thing last week, some lack of motivation and needed personal time. I feel tired but still ready to work out. It will pass like it did for me. You could catch up on other things if you're really not up for working out today.

Side note: We have a commercial that's been playing regularly about joining a gym. It gives examples of what people do that isn't exercise, then talks about "real" exercise. One of the examples of non-exercise was washing a car. I don't know about you but that really can be exercising.