One question you might ask yourself at the end of your workout is "If I still feel energetic at the end of a workout, should I keep exercising?"
Remember, feeling great after a workout is a signal that you've put in a hard day's work, made progress, and haven't overtrained.
Usually, one should never feel completely drained after a workout, because that can indicate overtraining. There is a fine line between developmental training and overtraining. You should feel like you've worked hard, but not entirely exhausted.