Each player had three different stats: energy, mood and karma.
Energy ranged from 0 to 5000, and was delpleted every time you did anything. When your energy got very low, you got a popup message before every move you made, which was incredibly annoying. Consuming food and drink gave you more energy.
The mood and karma stats affected your chances of making stuff in the game (and how many XP you got when you did), and were altered by using various objects.
All three stats could go negative (as above - although negative energy get annoying quick because of the popup) but none could exceed their maximum values (well, at least after an early bug-fix ;).