1. The working routine you build up in the elongated crunch period simply isn't compatible with not having a hard deadline or seven. I get this myself after years of burning the candle at both ends and it is taking quite some time to beat it out of myself. The problem is that my work ethic has for years been fuelled by deadline fear, and those short times when the pressure came off a little I enjoyed the opportunity to procrastinate. Somewhere along the line that became normal but flipped: I find it hard to not procrastinate until there is some deadline pressure. This makes starting new personal projects almost impossible (well, not quite, I have ideas and make notes, sometimes even get around to trying a PoC, but staring proper implementation is the difficult point).

2. Common, garden variety, depression. This is seen a lot in circumstances you describe. It can be very difficult to sort due to how much the causes and effects can vary from person to person. Don't expect doctors to be able to help long term as the problem is often not really medical, apart from extreme cases where you might be given something truly mind altering most of what a doctor will prescribe is simply intended to prop you up a bit while you work on the problem. From personal experience of a very bad year or so in my life (over 15 years ago now, heck I'm getting old!): I found talking to a councillor and select friends/family were key.