its always a hard judgement call to make, even harder without seeing – and without having the joys of comparison and experience.
If you want to avoid going to vet at this point, then Weigh and monitor day to day – more than 10% bodyweight loss in a week, and I’d be concerned, 20% I’d be thinking about humane endings
they can get over stuff quite magically though.
piloerection is a classic stress sign – if the stuff around the eyes is red and crusty, then that could be the ‘red tears’ and another classic stress sign.
if you got into constant head tilt, staggering, cessation of grooming leading to yellow/greasy belly and/or head then I would be more concerned and consider humane endings
this is a pretty good video to watch: https://www.youtube.com/watch?v=qDeOV9qPEbk
(for reference, not a vet, but a former licencee and care and welfare officer in a rodent lab, so day in day out observing condition of rats and making these calls all the time)