feeling great; refreshed
Describes a state of feeling physically and mentally refreshed, often after exercise, a bath, or a good night's sleep.
After working up a sweat on my morning jog, I felt great.
I feel refreshed after soaking in the hot spring.
爽快 is an adjective meaning 'refreshing' or 'exhilarating', while 気分爽快 is a noun phrase specifically meaning the state of feeling refreshed.
気分 means 'feeling' or 'mood' in general; 気分爽快 is a specific positive state.
Compound of 気分 (feeling, mood) and 爽快 (refreshing, exhilarating). The exact historical derivation is uncertain, but the combination directly conveys a state of refreshed feeling.