What do you do when you’ve lived with poor sleep, but now you know you need to learn better sleep habits?
You have limited mental resources. If you really want to get stuff done, conserve them, and use them wisely.
Self-discipline is a muscle, and like any muscle, without exercise it atrophies. So exercise it.
One of the toughest things about getting back in shape is not overdoing it to the point that the exercise makes you physically ill. Backing off a little is better than vomiting mid workout, I think.