For me, it NEVER gets fun. I've been fit. REALLY fit. And it always sucked. 

Runner's high? GTFO. 

The pump after lifting? GTFO 

Never once after a workout have I said, "Oh, I feel great!" 

It sucks. I hate it. I have to put in way more effort than most to get mediocre results. 
I suppose it's better than dying, even if doing it could kill me anyway. 😝