The timing of his sudden lack of communication (right after you slept together) really is super odd and a big red flag, but I think I would probably give it a little more time, just in case he really is feeling terrible. It’s possible that that really could be keeping him from responding like normal just from feeling weak and lethargic, and I think people tend to be a little more self-centered when sick (not thinking about how others’ might feel) just because their own pain is so noticeable to them right then and he really may just be sleeping a lot.

So, my advice would be to just ride this out for a few more days. Don’t ask him to hang out, and I probably wouldn’t even bother texting him until he texts you once he feels better since you’ve already let him know you hope he feels better and to let you know if there’s anything you can do. He can only have a cold for so long and THEN you’ll be able to really gauge his interest by how well he communicates after that. If he’s still taking forever to reply or not seeming to be interested after he’s feeling better, then I would back way off.