Agreed on it probably being easier if it’s something you’re used to and not actively in pain.
Not everyone gets a lot of FOMO, so I could imagine that might also not be much, though.
I mean, maybe you just mean frustration/sadness that he can’t do as much as other people, or to do specific things he wants to do. And I could imagine that could be just incredibly tough. Like all sorts of people with severe, debilitating conditions. But FOMO is kinda a different (more childish) thing than that.