I'm sure you've had a day where you've felt invisible, everyone does at some point.
I was having an especially invisible day, where I narrowly missed two nasty accidents on the highway with people merging into my lane, completely cutting me off. Considering where I live, this is more of a norm than not. I didn't think much of it at first.
But once I got to work, I was walking into the building behind someone, a stranger, who looked briefly behind themselves right at me and let the door slam behind them anyway. No apologizes to me either or even acknowledgement that I swiped in behind them.
Annoying, but again, just brushed it off. But later that morning when I had no less than 3 people bump into me while walking into a hallway, I started to get paranoid. I'm not a large person by any means nor were they. You'd have to go out of your way to run into me in that space... or just not see me.
The coat of invisibility continued as at lunch one of my gfs walked right by as she was looking for me and didn't even hear me when I called her name at first. Apparently cloak was getting more powerful as in it was making me unheard as well.
The final straw was in the bathroom when I went to wash my hands at the automatic sinks. It took 2 sinks before one "saw me" and I was able to get running water. I checked to make sure I still had a reflection, just in case.