Lanefan
Victoria Rules
Yes it is.There are limits. There are things you don't do to a PC without the player's consent.
Exactly what those things are will vary from table to table. But, a blanket, "Well you failed your save, so they get to do what they want," is not generally acceptable.
With a DM this can veer into abuse of authority etc., but if it's another player who in theory is your equal at the table, anything goes.
And on a broader scale, everyone involved has to realize and accept, up front, that bad things can and will happen to their PCs. They could die, they could lose levels, they could be put through the wringer and handed back to you as rabbits, they could be corrupted, dominated, mind-controlled, aged (up or down), imprisoned, and any number of other "not fun" outcomes. The source of these bad things is usually the setting (via traps, curses, etc.) or the opposition (via spell, inherent ability, or weapon); but sometimes it could be your own party or even yourself.
This is the flip side of all the good things that much more often happen to PCs - they gain fame and wealth, they gain levels, they gain powers, social standing, knowledge, experience, and so forth*.
* - and, ultimately, the ability to inflict all those bad things on to others if they so choose.
