Out of pure interest does anyone have, or is it possible to have, unipolar mania or hypomania? or is that energy not sustainable?

It is possible: Yes, people have symptoms of hypomania or mania very often, without a significant down period.

A Manic Episode : Acute mania can be prolonged. It's quite dangerous and potentially fatal. The symptoms include racing thoughts, delusions of grandeur, loss of impulse control, loud and pressured speech, severe and prolonged insomnia, spending sprees, irritability, hyper sexuality, hyper religiosity, etc. The person may engage in behavior resulting in injury or death.