Re: Relaxing Aiki vs Yoga.
On a different tack I could agree with you, TongBui. A friend of mine, while riding with me as I wove through traffic along the D.C. Beltway told me that the experience was exciting, yet calming. Keeping at a clip of roughly 70, it helped that I drove 100 meters ahead of myself. That, except perhaps the added speed, is a good way to drive because it allows for better anticipation of driving conditions, instead of reacting to every brake light you see.
Translated into Aikido, when I have the right feel for timing, my balance, their balance, momentum, and awareness of the nearest & ready uke, randori can be both calming and exhilirating.