random sadness

does anyone ever feel this sometimes? I lowkey have like, no real problems and things to be sad about, then randomly - It just hits. While I'm sitting at bed or something like that, it's really annoying, especially since I wanna keep up my positive mindset, can anyone give advice on what to do when it hits? I'm sick and tired of feeling stuck sometimes, usually. It's even my reason why I'll lack motivation to do something, I just wanna be the best version of myself.