I have given my self level 4 health boost for 1999999999 seconds, and at random I take 5 HEARTS (10 health) of damage for no apparent reason, no mobs around, no fall, no suffocation, no drowning, no lightning.
Note the version is not 13w26a it's 13w26c
This ticket has been marked as a duplicate of MC-18976, in favor of the better description/information provided.