Yes, RELAXING is a Scrabble word!

Letter values in Scrabble US: R 1, E 1, L 1, A 1, X 8, I 1, N 1, G 2.

Is it a valid word?

RELAXING is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

become less tense, rest, or take one's ease
make less taut
become loose or looser or less tight
cause to feel relaxed
become less tense, less formal, or less restrained, and assume a friendlier manner
make less severe or strict
become less severe or strict
make less active or fast

Also: loosen up, slow down, make relaxed, slack up.

Not playable in Scrabble US: UNSTRAIN, UNLAX.