There's a moment where The Doctor has to think about the question being asked, and still continues to smile; "Yes. The vocal vibrations in your voice stirred the brain neurons that provoke emotion and thus feeling happier. Least for the moment."

See not magic - there's science behind hypnosis.

"I can't complain."

And he won't say it but he also probably felt the positive vibrations in the psychic forcefield around his head and allowed the vibrations onto the surface of his mind.

Which maybe - for just a moment - Angel felt a slight shield resistance at first.