I'm one of those who sometimes struggles to function and I have days where I'm happy, more so recently. We have had people in the past who have a full time job and people have no idea they have depression. It's known as high-functioning depression. My partner is like that. He role at work is safety-critical and he does a brilliant job, everyone who works with him says that. Yet he has severe depression and anxiety and only recently finished counselling. He looks after his children, works full time and volunteers a couple of days a month. It's a lot more common than you think lovely.