Negative Con and rolling HD

[Mouseless]

So i have an old Elven psychic and my con suffered a lot from that, its 6. (yes i know horrible choice but i love it)
But now I won't to know if I risk dying by rolling badly on my HD, 1-2 would make me lose HP each lvl, or if it goes min. 1?

But that is not the end of my old man's problems because he just got disease which made him lose 2 con (yea he is gonna die in about 2 day)
But he just levelled up, and if HP per level is minimum 1, do i then use my normal con score or my new to figure out when i hit that min. 1?

[Thebazilly]

The minimum HP you get on leveling up is 1. You can't gain negative HP when you get a hit die.

Your Con score is also retroactive. If your Con goes up or down, your HP fluctuate with it. So you would use your current Con score when determining your added HP for leveling, AND you'll have to subtract HP from your maximum.

Since your Con went down by 2, that's a -1 to the modifier, for -1 HP per level from your normal amount. If your character is healed back to 6 Con, you'll get +1 HP per level.