Feeling exhausted after workouts?

Sometimes after our workouts I feel completely wiped. (I refer to this as "blowing a gasket"). It's all I can do to drag myself to the car and drive home, which is luckily not very far. Usually it's a sprint workout that will do it. Let's just say that it makes it hard to get work done the rest of the day... Does this happen to anyone else? Any suggestions, other than "don't swim as hard," which seems to be defeat the reason why I am there in the first place? (It doesn't seem to me that I am swimming harder than anyone else).