Many emotions drive the rectification of a bodily need – for example, hunger drives seeking nutrition. Nutrition is a finite upside and the strength of the urge is proportional to the urgency of fulfilling that need. There is very little that science can say on this because it is impossible for a scientist to measure the strength of the urge. That can only be seen in the consciousness of the urged. When two urges that drive seeking a finite upside coexist (say you are hungry and tired) then the relative strength of each urge determines in which you order you will seek to rectify the respective bodily need. We could say that the greater urge is dominant.
Some urges drive escaping an imminent infinitely negative outcome that we usually call death. If two urges coexist, where one drives seeking a finite upside and the other drives escaping an infinitely negative downside (say you are tired whilst fleeing a predator), then the former can never dominate the latter. And the simplest way to ensure that this does not occur is to switch off all emotions that drive actions with finite upsides. I speculate that this switch is a primary function of dopamine in the human brain.
When you experience the dopamine rush that you get on a rollercoaster, it might feel like a euphoric positive emotional experience, but it probably arises through the simultaneous switching off of all negative emotions (hunger, tiredness, pain, etc.). Your brain interprets the steep drop down the initial swoop of the rollercoaster as a near-death moment, and it responds by switching off all awareness of such negative emotional experience. It is quite difficult to come up with an explanation of the evolutionary origin of a positive emotion.
Humans seek emotional fulfilment through acts of pure imagination (e.g. imagining being in bed with the object of your sexual fantasy, or having an imaginary friend). Another seemingly paradoxical way to achieve this might be to imagine a near death experience. It is conceivable that, by doing this, you could train yourself to trick your brain into releasing dopamine, and you could do this at will. This would achieve a euphoric emotional rush – the best conceivable emotional outcome. If human wellbeing is measured in emotional outcomes, then it is rational to do this. In fact, once you had perfected the technique, it would be rational to do it for all your waking hours. People who are not psychotic tend to imagine that the manic phases of someone with psychosis must be hell. But imagining hell may be the whole point. If that is the case, then psychosis is a motivated self-deception with the rational objective of seeking a favourable emotional outcome. Psychotics often say that they only feel truly alive when manic.
It is a source of frequent frustration for psychiatrists and family members of psychotics that they relapse by refusing to take their medication. But if this model of psychosis is correct, then it is even rational to stop taking your meds, since the “cure” is cutting off an avenue to positive emotional experience. Only the psychotic can know whether this is a price worth paying or not.