If you've entered the "burned out" phase, it'll be very often high anxiety, low energy, sleep problems (either very short nights, or very long nights, coupled with large naps and somnolence through the day), feeling angry or depressed, feelings of dread. You stop enjoying what you used to enjoy, and it's basically easily confused for "just depression" (which should also be treated) Your body just lets go of all non brain functions and focuses on your mind. And your mind is feeling like shit, empty and useless.

If you're at the "right at the edge of it" phase, it's rather obsessional focus, trying to please everything and everyone, high feelings of responsibility and duty (even if nothing will happen if you're gone), stress (both the "good kind", the one that everyone believes is perfectly normal to have when you have something important to do, except all you're doing is making a shitty CRUD app right now, and the bad kind, where going to the office fills you with dread), not enjoying what you used to enjoy but saying "it's okay, it's just temporary" when you've not touched that backlog of games in 6 months.

I didn't enjoy anything anymore. I didn't enjoy movies, activities, programming or hobbies. I also slept a lot, like 10+ hours a day. I would just fall asleep while sitting on the couch watching something with the wife. And I just felt like I was empty.