I somehow disabled the animation that shrinks and twirls the window to the dock. The one that shrinked the bottom part of the window and twirls it all the 
ay down. Now it just shrinks and goes there /the worst explanation ever :-D/

So how to re-enable the default minimize animation?!

Just open System Preferences, then select Dock (Top middle)

You might have it set on 'Scale', the twisty effect is 'Genie'

hth.