What’s the price for dying?
Path of Exile mentions that death carries experience penalties on high difficulty levels. Can the experience penalty incur in a level down? What if you already had allocated your passive skill point?
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From this answer and its first comment, death cannot make you lose a level.
No, you cannot lose a level by incurring the experience penalty upon death. Worst case is you lose all your XP accumulated at your current level and therefore having 0% XP at your current level.