Running is like stimulant, but swimming could be like depressant?

I feel like that. Because when I went running after work, I had hard time going to sleep feeling so awake like having many cups of coffee, but when i went swimming in the evening, I could be relaxed and sleep better. My heart rate won't drop to normal for several hours when i go running, but when i go swimming, it drops to normal much quicker than after running. 

Both exercises for me usually last about 40 mins. Maybe it's something to do with difference in impacts that your body takes. Running is extremely high impact on your body where swimming is very low impact on it.

Maybe something to do with cooling system you are using for each of exercise. For running your body is air-cooled during exercise which isn't most effective especially during muggy summer evening. During swimming your body is water-cooled efficiently and it cannot be overheated. Often time, by the time i'm done swimming, I feel rather cold with sneezing. 

Even if intensity of both running and swimming might be similar, but the recovery of your body and heart rate could be significantly different because of these reasons, I wonder.