"[P]eople who suffer from depression tend to have more REM sleep than would be considered normal." #readingToday
Interestingly (and perhaps unhappily), people who suffer from depression tend to have more REM sleep than would be considered normal. Negative memories are the ones that seem to be really protected by REM. There isn't much work on positive memories, but what is there hasn't shown a big protective effect. So if sleep does selectively preserve positive memories against decay then it doesn't seem to do this to such a great extent as it does for negative memories. Is it possible that excessive REM could be making depression worse—or at least keeping people in a low-mood cycle by selectively boosting memory of all of the bad things that happened to them, while more happy (or at least neutral) thoughts are allowed to wither away to nothing?
(Moon+ Reader Pro v2.3.3, The Secret World of Sleep: The Surprising Science of the Mind at Rest (MacSci))