What is these mushrooms in my indoor pot?
They do look a lot like a common mushroom called "shaggy mane" mushroom (Coprinus comatus). This may not be a correct identification though, so do not eat them.  They are widespread around the world, but usually grow outside.

Yes it is amazing how rapidly the fruiting body of many fungi can grow. I am providing an interesting Wikipedia link with more information. You can also search to find other images using Google images online.

https://en.wikipedia.org/wiki/Coprinus_comatus