Apologies for the late reply, but maybe I can still help :)
Not to worry, your Spotify playlists haven’t disappeared - it sounds like you might’ve accidentally created a second account and signed into that one instead. I'd recommend checking out the FAQ page "Can I create multiple accounts?" here for more info.
If you’re definitely logged into the right account, but you’re still not seeing some playlists, I’d suggest reading this Spotify Answer for the correct steps.
Hope this helps!
LukeRock Star 17
Help others find this answer and click "Accept as Solution".
If you appreciate my answer, maybe give me a Like.