phrases - What is a word or expression for a person who feels free?

'Uninhibited' would indicate being free of any limiting factors.

You say 'could do anything,' though, which implies much much more than mere lack of inhibition. The ability to do anything is what's known as 'omnipotence.'

"I'm feeling omnipotent this morning!" is a strange, but humorous thing to say. If you would like to describe someone who takes unnecessary risks due to such a 'can do anything' attitude, a phrase commonly used to describe young men is '10 feet tall and bulletproof.'

It all depends on the nuance you want to capture.

• Next Where did the T-Rex come from?
• Previous film techniques - First use of on-screen text messages, like in Sherlock and House of Cards