It is normal. We recently finished a big project at my company. I barely had any sleep during the process. It took me 1-2 months to recover and begin doing useful work again. Just take it slow.

If in addition to being burned out you don't like what you are working towards, just choose a different goal. I found that working toward Artificial General Intelligence is a very motivating goal. I have been pursuing it for the past few years and I am yet to grow bored with it. The only tricky thing is there's a lot of bs surrounding the subject, so you need to learn to navigate it.