You wouldn't really be able to tell when he is sick. Because he would just sleep because he doesn't feel good. The way you would probably notice is, he'll slip up when his half asleep and say something like.. "Mc.. let me sleep.. I don't feel good"
You would also find him sleeping in your bed when his sick. He finds comfort in you. So anything that smells like you will make him sleep peacefully.
He would hate the way medicine tastes. And I mean hate. He would refuse to take it. Saying some like "Oh I'm a demon.. that medicine won't work for me." Or "If you think a little sickness will kill me your wrong."
Once he had slept through a whole day before when he was sick. Let's just say Beel was worried about him.
