Is there such a thing as a sickly cat who isn't actually poorly but stressed or just...sickly?

[BikeTart]

Female tartcat has always been the more sickly of the two. Maletart is as robust as they come and has never been ill (they're 10).

She has bouts of being sick and we're in one now. Last time I took her to the vet and he checked her out, gave some meds and a special diet plan . All good. But she's been sick yesterday and today ON MY BED.

Advice from vet was to give her some catmalt stuff as they're Raggies and she is the bigger moulter of the two and I think she swallows more hair and this seems to help.

But, has anyone here had a cat who just tended toward the 'sensitive' end of healthy?