The exact same thing happened to a mate of mine.
His face went a weird green/yellow/pale colour, all blotchy.
He looked like one of those zombies from a poorly made horror movie.

We figured he might've been allergic to fertilizer used in the weed growing, or other such substances as he only got affected from one specific dealer of mine.
To cure it I just gave him a load of oranges (vitamin c) and then went for a walk.

My advice, use a different dealer.