Sleep debt itself is a weird metric. You can’t “pay it back”, lost sleep is lost sleep, period.

The body doesn’t keep track, the body just complains. You might feel weird if there is a dramatic change to your sleep schedule.

Think of bad sleep or insufficient sleep like an injury. In ideal conditions your body heals it at a certain rate. You can make it take longer, or you can even make the injury worse, by not taking care of it, but you can't make it heal faster. And at some point, if you're consistently not taking care of it, you'll make part of your injury permanent.

Similarly with sleep, it's not a bank balance, it's damage to your body and brain that you need to repair. And you can only repair the damage with good sleep. You have to get good sleep until you feel better, and then you'll know you have recovered.

And if you consistently get bad sleep for too long (a week or more), your brain and body will be permanently changed. Like a permanent injury, you'll never fully recover some of the damage. It's hard to overemphasize how important good sleep is to your short- and long-term health.

Sleep doesn’t work like a health bar in a video game.

Different stages of sleep have different efficiencies. For instance, passing out drunk doesn’t count as sleep. You body is still active in digestion which can prevent a good sleep, or intoxication can prevent the brain from going into deep sleep.

Sleeping is an activity. Humans are just weird for closing both eyes and both sides of the brain at the same time, but it doesn’t mean that we shut down completely. Most animals do not sleep this way If we could experience partial sleeping like animals, we’d probably understand better what a good sleep is…

I don’t remember the source, but I’ve read that, while getting a good night sleep for a couple days feels much better, it takes 9 days of good sleep in a row to recover as much as you can from sleep deprivation. If I recall sleep flushes out chemicals that build up in your brain, they can only build up so much before it’s saturated, and it takes the 9 days to fully catch up on flushing them out.

It sounds like the biggest thing that would help you is managing your caffeine consumption. I went through caffeine withdrawal a few times before deciding I didn’t like it and setting the following boundaries that have helped. First, no coffee/energy drinks after 12 hours before I want to sleep. So I go to bed at 10pm, I have all my coffee drank before 10am. This gives your body a chance to process most of the caffeine so it affects your sleep less. Second (and the hardest if you’re already used to daily caffeine) I try not to drink caffeine two days in a row. This keeps it from building up in your system, which keeps your tolerance low, which also means it feels like a super power when you do drink caffeine.