Wide Asleep

Twice now I've tried to read the passage in Jason Elliot's book An Unexpected Light on Sufism, a mystical branch of Islam, and both times my eyes tear up, or almost close involuntarily as I fall asleep, and prevents me from reading the whole passage or even remember the few words I have been able to read. I have noticed this happening when I read certain profound passages in other books as well. What is this phenomenon? It must have a name. Perhaps I am unready to be made aware of this knowledge. Most likely though I'm just tired. But it's interesting how the mind invents deep mysteries where there may be none.