Having had devastating, painful experiences with depression and mood issues (pretty much since childhood) I can only say for me, I can barely function normally when I'm lost in ruminating thought. It's almost like having a microchip in your brain that's on a loop telling you how crappy you are, reminding you of bad memories (you don't even get a break from the searing torture and pain in your dreams). You feel exhausted and it's very hard to take proper care of yourself.
However, there are people out there who are functioning addicts, who can uphold good jobs and still be in the grips of alcoholism (for example) yet still, to the outside world, seem perfectly fine.
So, although I don't think Meghan is the most genuine of human beings, this could be what's happening. That old saying, you don't know what someone's truly like till they close their front door.