This internet/text acronym "HIYH" stands for "Helps If You're High" that could be use when trying to explain or describe something, possibly while being high themselves. It's similar spelling to the word HIGH itself is very fitting.
Redditor A: After all my studies of science and the nature of the universe, I have come to believe that the fate of all matter and energy is to be destroyed in order to be created again in the big bang.
-Redditor B: Wut.
-Redditor A: HIYH lol.