<Snipped quote by GalaxyRaider>
All of those things that mom said.... what if she was right? What if I really am just a machine deluding itself? What if I’m not really alive?
I know it's a scary thought, but you have to take two things into consideration. One, the "delusion" actually being real. Unlike Data's thought experiment, Melody didn't actually experience an alternate reality, just an internal crisis. Two, the fact that you feel at all, and care about the possibility, kinda disproves the possibility in itself, don't you think?