I know exactly how you feel, and I live with my BF.
He's been at football today, which is ideal as I'm studying for my final exam, but I've felt dreadful all day.
It's hard to explain.
Solitary, in a bubble, not real (as you said).
I'm not depressed, and going out doesn't really help.. I don't know what it is really.
Sometimes I feel it, other times I don't.
The BF will be back shortly, and it'll go away then, but I don't understand it. I'm very confident, happy, run my own business and have plenty of Uni work to do, but I feel very odd some days.
Also, I don't know about you, but going out and doing something, even if it's social, can make me feel worse! Unless it's with someone I know well.