Mania does not need to have psychosis.

Mania will have a significant impact on your life. Hypomania might have an impact, or it might not.

I've never been manic. My hypomanias are great though - I'm more impulsive but I've got various rules for myself set up that I follow to help curb that. But I don't lose touch with reality or my life, and I can maintain my life - my job, my home life, my social life, my finances - none of those will be significantly impacted by my hypomania.

To me it's probably the biggest distinction - mania will often cause lots of difficulties with your normal life, but hypomania won't have such large consequences. I also think that hypomania can be fairly easy to "hide" whereas mania... will likely be a lot more noticeable.