If he can do any art at all, he can do your art.

I'm someone who gets sick a lot. A LOT. I'm pretty much constantly tired and run down, and I've always been this way. So what I do is only take one, maybe two commissions at a time, and work on them any chance I get. Just finished one yesterday morning when I woke up and wasn't feeling too bad, even. And if I'm particularly bad off, I just don't take them fullstop.

He's yanking your chain, even if all these times he's sick are legit. If he's too sick to work, he should refund.