I get that a lot too when depressed. Sometimes I wonder if it meets the criteria for catatonia. I know not to sit looking into space, but sometimes it's not a choice, I'll just lose ten or fifteen minutes at a time. Like being in a hypnotic trance.
That defence mechanism of seeming normal is only a brittle veneer though and it doesn't stand up to much.
Hope you feel better today, Melissa. I did read your other thread, and I know it's been horrible for you lately.