I'm thinking it's not a bug (as A he's only had 3 bouts of diarrhoea- though I do understand it's painful) and B no vomiting.
I've given him Imodium and hopefully that'll work- he seems to think it's alcohol withdrawal symptoms? He was only drinking 1-2 ciders a night for a while (I don't drink myself but he wasn't ever drunk so I wouldn't say he has alcohol withdrawal?).
I'm a literal germaphobe so this is my worst nightmare, we all get random diarrhoea every now and again and his mood is fine/laughing etc but I'm so scared he'll start vomiting and I'll get it!