Hypomania is when you have trouble controlling urges and impulses. This manifests itself in many ways including indulging in acts that could put your life in danger or risk financial ruin, alternatively it can lead to thoughts of paranoia or overprotection as well that would normally be perceived rationally. Sleep will be unstable with some nights substantial oversleep and others substantial undersleep.
Mania is when you lose complete control of how your mind works and are unable to control urges and impulses. This manifests in uncontrolled racing thoughts, breakdown of determining reality, and ultimately psychosis followed by catatonic stupor. Sleep will be erratic to the point of non-sleep and for a week followed by perhaps sleeping a full 1.5 days completely in deep sleep mode.

My theory on depression:
In worst case scenarios extreme mania results in extreme and long depression after. Whereas slight hypomania may not result in any form of noticeable depression. The effects of slight hypomania is mainly determined by your natural mood state. If you are depressed most often than a bunch of hypomania may result in a more noticeable depression.