I think it depends on the child, if they are more prone to being anxious then they'll feel it.
As your son is old enough don't try to hide it, but explain about your illness to him it will be easier for him.
I have 3 kids 15, 12 and 5 and have explained it to them. If mummies crying it means mummies sick, that's how my 5 yr old sees it and she's been coping well with me in hospital because she knows I'm a different mummy when I'm well and she wants that mummy.
I have found that my kids are very hard headed and they both now about my anxiety disorder but they also know that I to can be hard headed as well and will not back down from a fight, kind of funny how that works if I have no control over something I tend to dewell on it but if I have the need to fight it I can. Anxiety is kind of a mix's bag as I tend to go to my horses for comfort as they to can feel it in me just like kids can.