Good posture also helps you breathe better, which can help you feel more energized and concentrate better. Your diaphragm doesn’t work right when you sit hunched over, so your breath gets more shallow.
If you ever need to talk a lot for work or some other reason, good posture is essential so your voice sounds good and doesn’t get tired too easily.
And it helps strengthen your core, which is good for balance and other things.
Live music does it for me. It’s best when I’m close enough to make eye contact with the musicians, and when the audience is into it too. It’s a total rush. If I had to pick between music and sex, it’d be music, hands down.
I can relate to the comment about swimming too. I imagine hiking, kayaking, or anything else physical that you really like could give you a similar feeling.