Interesting topic.
My company takes sickness into account with different factors when they have to make people redundant.
Unfortunately (in these still uncertain times) this makes me come to work when I am sick. Especially when we are away from base and there is nobody to replace me.
I do not think your "old" company will say to the new company where you\'re applying how many sick days you have had. This is confidential.
So if you don\'t mention it they will never now.
If there is no escaping because of i.e. an operation or other serious problem you\'ve had and you have to mention it I don\'t think it will be a problem if you\'re healthy again.
In general: you don\'t have to tell everything.