I had a horrible day that not even the arrival of some cool new photography "equipment" (aka toys) could make better. After I played around with my new fisheye lens and IR filter outside, I wanted to take a shower (hot, humid, sticky day), but it took me about four hours to make it from the living room to the bathroom. I spent most of that time curled up in bed crying and feeling invisible. This has been a lifelong issue, and sort of a family curse. My mom is virtually invisible (which makes me angry when I see people totally ignore her). My dad has used his ability to be unseen and blend in to be a very effective hunter. My brother and I have both experimented with it -- great for when you are doing anything on the slightly shady side (in our younger years only, I swear!)

I don't know quite how it works, or what triggers it (when it is unintentional, like now), but it is some sort of psychological phenomena.