I've had a similar experience. I'm thinking it's because when I'm tired, I literally don't care about anything beside being tired so, a lot of the time, all the depression and anxiety stuff takes a back seat lol. Also, I read that sleep deprivation affects serotonin levels in the brain, so maybe that has something to do with it too....

Also, has anyone ever felt super paranoid as they get ready to sleep/at night? This has been happening to me for a few weeks now and it's quite bothersome.