Here is a mood chart that shows various mental states that can come with bipolar disorder (manic-depression):
+5: Psychotically high mood. Total loss of judgement, exorbitant spending, religious or other delusions or hallucinations.
+4: Semi-psychotically high mood. Partially lost touch with reality, incoherent, no sleep, paranoid and vindictive, reckless behaviour.
+3: Very high mood. Inflated self-esteem, rapid thoughts and speech, counter-productive simultaneous tasks.
+2: High mood. Very productive, everything to excess, charming and talkative.
+1: Happy mood. Self-esteem good, optimistic, sociable and articulate, good decisions and get work done.
0: Mood in balance, no symptoms of depression or mania.
-1: Sad mood. Slight withdrawal from social situations, concentration less than usual, slight agitation.
-2: Low mood and anxiety. Feeling of panic and anxiety, concentration difficult and memory poor, some comfort in routine.
-3: Very low mood. Slow thinking, no appetite, need to be alone, sleep excessive or difficult, everything a struggle.
-4: Extremely low mood. Feeling of hopelessness and guilt, thoughts of suicide, little movement, impossible to do anything.
-5: Severest low mood. Endless suicidal thoughts, no way out, no movement, everything is bleak and it will always be like this.
It is okay to be at zero where mood is balanced. The ideal position is being at +1 (this is called euthymia or good mood). The scale is exponential, not linear i.e. being at 5 is much worse than being at 3.