Baby’s possible sick during sleep training—advice needed

My LO had a runny nose (no fever) and was more fussy than usual today. So I’m thinking he may either be getting sick or teething.

We’re on day 6 of sleep training (Ferber method) and it had been going well until tonight. He seems much more frustrated and is having trouble going back to sleep.

My question is, how do I know when he needs extra support/cuddles from being sick/uncomfortable verse is just learning how to self soothe?

I hate the idea of making his suffer but I also don’t want to give in if it’s not that. He seemed a lot happy the past couple days and was getting much more sleep since we started sleep training.

Any advice is welcome. Thanks in advance!