Mustrum_Ridcully
Legend
The loss of levels due to death can be explained by the traumatic "experience", some kind of coma-based brain damage and similar things. 
Maybe it is a "security" method of the gods/universe to avoid that people remember the time when they were dead. (And only True Resourection is powerful enough to find the exact memories to be erased).
If you use this interpretation be aware that you have to change some roleplaying aspects - someone back from the death might have forgotten what happened the last "level", so you must explain him why he was so stupid to start an attack with a "terrible, fire breathing dragon".
Hmm, I think I will implement this a bit in my upcoming Dragonstarbased campaign. (I like my own idea...
)
Mustrum Ridcully

Maybe it is a "security" method of the gods/universe to avoid that people remember the time when they were dead. (And only True Resourection is powerful enough to find the exact memories to be erased).
If you use this interpretation be aware that you have to change some roleplaying aspects - someone back from the death might have forgotten what happened the last "level", so you must explain him why he was so stupid to start an attack with a "terrible, fire breathing dragon".

Hmm, I think I will implement this a bit in my upcoming Dragonstarbased campaign. (I like my own idea...

Mustrum Ridcully