Hi Zero,
I guess the ironic thing about my life is that I grew up in a family of workalohics, with "idol hands being the devil's workshop."
For a long stretch of time, I was in school and working 2-3 jobs, so even when I wasn't working, I was at the library or buried under stacks of books.
And even when I "cut down" to "just" one full-time job (for a while, I also worked another job on my days off), I then filled most of the extra time with church activities. At that time, I had left school and was just working, and because I didn't have to study in all my free time, I joked with my family that it almost felt like being retired ("Seriously? All I have to do now is WORK?")
This is why I say I'm an introvert who can masquerade as an extrovert when needed, and also the reason why I never realized I was an introvert up until a few years ago. I'm finding the secondary discussions here about anxiety to be interesting, because I know I suffer from anxiety but I'm not sure to what degree it would be diagnosed. But the way I was brought up, responsibility trumped everything else, and so I learned to put the bulk of my fears aside (or hide them well.)
I finally realized I couldn't keep up the break-neck pace that the rest of my family has managed to do all their lives, so aside from work, I cut back some of my volunteer activities, which is why I always chide and fight with myself for being so "lazy" -- compared to the rest of my family members, I'm a couch potato.
People also saw me in very isolated environments and assumed that the times they saw me were the only times I ever did anything in life, lol. They didn't really have an interest in what my life was really like, so they just assumed I "wasn't doing anything else" and that I had all the free time in the world.
I wouldn't even need to come up with an excuse, I'd just have to tell them I had other obligations, even if was just trying to get some much-needed sleep between jobs or classes!