Yes, PYROSIS is a Scrabble word!

Letter values in Scrabble US: P 3, Y 4, R 1, O 1, S 1, I 1, S 1.

Is it a valid word?

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

a painful burning sensation in the chest caused by gastroesophageal reflux (backflow from the stomach irritating the esophagus); symptomatic of an ulcer or a diaphragmatic hernia or other disorder