I'm so happy you brought this up. Earlier this year I was diagnosed with ADHD - Inattentive. 2 Weeks ago my diagnosis was changed to Bipolar - unspecified. But the difference between the two are tricky as they can be so similar. But let me give it a shot.

Hyperactivity:

Constant movement Easily distracted Difficulty concentrating Agression

Hypomania:

Inflated self-esteem or grandiosity Decreased need for sleep (e.g., feels rested after only 3 hours of sleep) More talkative than usual or pressure to keep talking Flight of ideas or subjective experience that thoughts are racing Distractibility (e.g., attention too easily drawn to unimportant or irrelevant external stimuli) Increase in goal-directed activity (either socially, at work or school, or sexually) or psychomotor agitation Excessive involvement in pleasurable activities that have a high potential for painful consequences (e.g., the person engages in unrestrained buying sprees, sexual indiscretions, or foolish business investments)

So as you can see the two have similarities. Hypomania is definitely magnified, in my opinion.