Falling up can be indirectly compared to the act of falling down, and to a lesser extent falling over (but not under).
One can experience upfalling when losing one's footing whilst climbing a wall or other such vertical flat surfaces. If appropriate measures are not taken, it is in entirely possible to fall into Earth's atmosphere and implode in spectacular fashion. It really is a sight to behold, in some cases more thrilling than an asteroid shower. Though not for the victim, obviously.
There are numerous instances of people falling into outer space, though few have been recorded. In some cases, the victim's fall is broken by passing aircraft or hot air balloon, which generally results in midair madness -- which, incidentally, became the subject of a Microsoft video game in 1998. For this reason, planes are now fitted with underside wipers which activate upon impact. The resultant remains are swept into the cockpit and recycled as airline food (it's like real food but horrible and more expensive).