Hi slobone,
Forgive me for responding before marik, but this is an important topic, so here's my two cents.
Sitting low can do wonders for tone production. However, there is more stress in lifting the the weight of the arms against gravity. Sitting higher can facilitate velocity, but also tends to produce a thin, bland "gray" sound rather than the richer tones when sitting lower.
Before I retired, I took a couple of seminars in office ergonomics from two different groups involved with workers compensation claims and employee rehabilitation. Ergonomics also became part of my management portfolio at two different companies. I was especially concerned about tendonitis and carpel tunnel syndrome developing in workers sitting at PCs where the workstations were not configured ergonomically. Once we helped the employees with those issues, claimed decreased almost to nothing. So the principles work. And yes, from the pain you experienced, keyboarding without attention to ergonomics can indeed lead to injury. When you think about it, a computer keyboard shares a lot in common with a piano keyboard.
So here's the thing: (And yes, I have an adjustable artist bench at home and practice what I preach.) You would best sit on the front half of the bench or chair in front of the piano. Your elbows should be LEVEL with the keyboard, forearms PARALLEL to the floor. Your wrists should be extended NEUTRALLY--not at an upward or downward angle. You cannot judge this for yourself. You need someone to stand and look at you actually sitting in profile at the piano who can better determine whether you are positioned as stated above, or not. This is exactly how I sit to play the piano now. For me, the question is not shall I sit high or low? Rather, it's: Am I sitting correctly according to ergonomic principles to maximize comfort and efficiency, while minimizing the possibility of pain or, worse, injury?
If you feel tightness in your arms or hands, here's a cure. Stand up away from the piano. Next, drop your arms and dangle and rotate them slightly back and forth, as if they were a couple of ropes dangling in the wind. Then swing them in front of you such that when they cross in front of you, they momentarily form an X. After you do that for a minute or less, you should be able to sit at the piano and continue on as if nothing happened. If not, give it a rest for 15 minutes or so. Never play through pain.
I hope this helps.
