Yvan's Affliction ???

Yvan's Affliction is eluded to in the dialogue ... and twice we see him basically pass out like he is a narcoleptic. Then there is the time when he goes to the water trough when they initially get to the cottage and seems to have some sort of spasm (all this thrashing). I do not understand what this all means in the film as a whole. Can anyone help me?

Maybe it is the explanation as to why he was institutionalized?