you have gained -1 hitpoints

[malkaviano]

Screenshot says all.

hp.jpg (196.72 KiB) Viewed 630 times

[Neptunetitus]

All I see is something about a small fuzzy paw in Uranus?

[Mobi]

This doesn't actually happen, there is some math error for the display of stat changes on level-ups. You gained hit points not lost them.