Manic people are overactive, rushing around continually without break; talk fast, too much and too loudly, hardly sleep; are short-tempered and often aggressive. Full-blown mania is usually characterized by a wild over-confidence and over-estimation of one’s ability, often combined with a paranoid belief that these abilities are being thwarted by other people who happen to be around.
[...]
For over-arousal to tip over into hypomania, the normal sensation of fatigue needs to be suppressed or over-ridden by an analgesic agent. The human body produces its won analgesics, of various kinds. The ‘high’ mood of mania is a secondary consequence of the ability to remain active without fatigue. Such an ability usually this makes people feel good, feel powerful, they are impressed with themselves. The analgesic activity means that there is a loss of perception of many of the negative feelings that accompany normal life, a blunting of the sense of shame, shyness, fear.

If mania is caused the inappropriate activity of some kind of endogenous analgesic that prevents fatigue, the question arises as to what this analgesic might be. An analgesic drug could be responsible, for example amphetamine which produces a state very similar to mania. However since many patients with manic symptoms are not taking any drugs, this strongly suggests that there is an endogenous or internally-produced analgesic substance which abolishes fatigue in the manic patient.
…
We can now suggest a plausible sequence of events leading to hypomania. In the first place, there must be a hyper-aroused, driven state leading to over-activity. Perhaps a young businessman is trying to achieve an almost impossible deadline and stays up night after night on paper work. At first he feels exhausted, but keeps pushing himself and finds that the more he does, the less tired he gets.

Normally, over activity would be stopped by negative-feedback from fatigue. But if hyper-secretion of endogenous opiates is present, these may have an analgesic effect that removes the negative feedback of fatigue. In the businessman’s body great floods of endorphins lead to immunity form tiredness, and a feeling of invulnerability. The businessman starts to feel that he is breaking though to a new level of ability — after all, he can work twice the number of hours as anyone else, he feels great, his mind is sharp, and the work he produces is great! He has no time for the slow dull plodders (such as his wife) who tell him he needs a break, a rest a sleep: they may need it, but he does not. He is clearly superior. He asks her to run a bath, this seems to take forever, and then when he gets in the water is too cold!

The businessman turns on his wife, and sees that she and the children are cowering in the corner as if he was some kind of wild beast. Disgusted at their feebleness he storms out of the house slamming the door. Perhaps he should go and find a prostitute instead of his wife — after all a man of his energy cannot expect to be satisfied by just one woman…

Hyperactivity continues, which provides the ‘stress’ necessary to stimulate further endorphin secretion. Overactivity is accompanied by diminished sleep. If over activity is so severe as to reduce sleep below the minimum necessary for human health (usually about four hours a night) and for several days in a row — then the patient might become delirious due to sleep deprivation. The delirium will then lead to classic ‘psychotic’ symptoms such as hallucinations, bizarre delusions, and jumbled speech (‘thought disorder’) superimposed on top of un-fatiguing hypomanic over activity.

So the full state of mania might emerge — over activity, lack of fatigue and psychotic symptoms. The businessman leaves his desk, roams the streets trying to enlist people for his new project, telephones colleagues all through the night, takes a plane to the central office (no time to waste!), harangues the chief executive for his failure to allocate resources to the new project and gets kicked out of headquarters. He realizes that the company are all in a conspiracy to hold back these new ideas. He has stopped sleeping, although he isn’t really fully awake — but in a fluctuating twilight state, finding it difficult to concentrate or frame thoughts.”