I often don’t have the words to describe a feeling. Worse than that, I don’t always remember having had a particular sensation before.
It can be frightening.
I’ll have to consciously tell myself “Those symptoms mean you’re tired” for example. I don’t believe it at first. It feels new, nameless, awful. But once I convince myself that ,logically, it’s “tired”, I lay down and fall asleep much to my own surprise.