Personally.. I need LOTS of space.
Space just being alone time, not actual square footage (ofc).
Like, in my bedroom. Or in my car, listening to music. Or in the bathtub reading a book.
Those are places I know I'm not likely to be intruded upon.
It's best when I live entirely alone, though that's not always doable.
It's just that 100% uninterrupted freedom, let my mind just wander the vast expanse of my internal universe. I hate getting jerked out of it suddenly - or being kept from visiting it for extended periods of time.
People knocking at my door, yelling for me constantly, or otherwise summoning me is a huge 'space invader' for me, indirectly speaking. As are many phone calls. I hate the phone. Text messages are usually ok, but even on my stressful days, I just want to be invisible, dammit. Let me recharge in peace!
People just 'showing up' at my house.. is unacceptbale 99.9% of the time.
Unless you're upset or something. I can make an exception.
Not that I don't enjoy the company of my friends, etc, but I definitely need to adjust to being around people, including them. So bursting into my space without warning, just, throws me off, and irks me. You'd rarely notice this, though I would tell you plainly at some point, not to just show up again. Nothing personal. Even just call or text from a few minutes away would be helpful.
For this reason I try very hard to understand the personal boundaries of others as well, regardless as to whether or not they make sense to me. They don't have to.
Really, I could go weeks without interacting person-to-person with a soul and be totally fine with it. Not sure if it's healthy, but it doesn't feel unhealthy.