I don't have any trouble motivating myself to get to the gym, the only problem I have there is deferring it too long sometimes. I feel better after a workout and shower than any other time. I like to leave at 1PM; today I didn't leave till 4. But I went and got in my workout.
I'd endorse that part about not trying to make up lost time all at once. If I've been away a week or more and then push too hard I will get a migraine every time.