That wasn't my point, actually.
Generally, people tend to get pissed if you try to keep stuff from them. And how pissed they get is directly proportional to how important it is.
If it turns out to be important, then it increases the feeling of helplessness if they couldn't be there for you even before they knew what it was. If it doesn't, then they'll still be pissed because they figure you couldn't trust them to be there for you at a critical time, regardless of what they could or could not have done.
In many ways, by trying to spare their feelings and spare them worry, you're kinda sending the message that you don't trust them not to freak out.
It's best to be honest, and it may even lead to you getting help - for example, in case your doctor can't convince Medicaid.
Just what I think, though.