Oh that... yeah I forgot you were over your CON limit. Yeah that's correct then. I just forgot you are in the same situation as me and several others. My buddy lost 11,000 the other night. That's hurts, but it's better than being erased or having an unusable character.
Wait till you get a follower and they die, and you die. Then you lose that + follower XP loss.
It seems a tad unfair at first... but we decided those punishments are actually quite appropriate based on what you have done. IE you have squandered your lives AND/OR you are voluntarily killing off what would be technically your best friend in the world (pushing them into dangers they cannot overcome etc).
We have been discussing the death penalty though for CON exceeders such as yourself and at much higher levels it's quite a devastating punishment. We might change that penalty to 500 xp / level. But only because once your at a high level and everything only gives you a small amount of xp / kill... it's hugely time consuming to regain ALL of that back. At lower levels losing 4 -8k is frustrating but not maddening.
So someone at 1st level would lose 500 xp
5th level would be 2,500 xp
10th level would be 5,000 xp
20th level would be 10,000 xp