Did you notice this after hopping into your car from Go-karting?
Jokes aside, my power steering felt really heavy as my power steering ECU failed and needed to get replaced. It's a costly replacement, but luckily I paid for warranty.
In regards to the very light steering, did you hit a pot hole or something recently? It's possible that your alignment is out - specifically, your toe. For something more serious, you may have bent something.