If the Exp penalty after any kind of Resurrection (See Death & Resurrection System for more details) would make you lose a level, you don't lose the level anymore, but instead your exp will be set to the minimum amount required to stay into the level you are.
The exceeding Exp, will generate an EXP DEBT (level 40 players are NOT included and can lose 1 or even more levels on ress. It really depends on the ress option chosen).

You won't be able to gain experience until the debt is paid.
To pay the debt, you just have to kill monsters, that experience earned, will take down the debt until fulfilled.
If you die again while still in XP DEBT, your next Resurrection will increase the XP DEBT you already had.