All Saves Have Disappeared

I turned on my laptop, started up the minecraft launcher, went to play one of my singleplayer worlds, only to find every single one of them gone. I must've had over ten there, both creative and survival worlds.

What I expected to happen was...:
All my saves show up in "Singlelayer", like normally.

What really happened was...:
There were no saves in "Singleplayer".

Steps to Reproduce:
1. Open Minecraft.
2. Press Singleplayer
3. Find no saves