Before returning mine I did try turning heart rate off to manual but it made no difference. My arm Just constantly ached. I have worn a Fitbit forever and now have recently bought a Fitbit Charge 3 (to replace the Galaxy Watch I returned) it has the heart rate sensor and I have had no problems at all. I'm curious if all the people who are experiencing problems, does your watch have the LTE function? Some research needs to be taken out by Samsung as this is an actual real problem.
It the tightness of the watch isn't the issue, then the only other thing I could think of is the sensors.
The most obvious thing to me is if your body is more sensitive to the light from the sensors, or more sensitive to something else.
I am having this too. I realized it how the watch is sitting on the wrist. When I bend my hand down, the bottom of the watch is pressed against the top of my wrist and is acting like a bar. Its putting pressure down on the wrist while your wrist is trying to push up to let you bend your hand. Its basically pushing down on the point where it is affecting the carpal tunnel. Its difficult to keep the watch from sliding to that exact spot and its causing compression.
I've been experiencing the same since 3 weeks. I'm using the galaxy watch since 5 months, so I thought watch was not the reason of pain. After the pain started I stopped wearing it for 3 days and the pain gradually decreased. But then when I wore it a day again, the pain started again the same night. It took me 3 weeks to understand this is due to the watch. This pain hurts a lot, starts at the elbow to the little finger and to the top of the arm. If I ignore the pain and continue to wear it, then the pain is terrible!
There is an old trick that my uncle, a retired Lt. Colonel has been doing for many years now. Affix the face of the watch so that it can be seen when you turn your wrist upwards. It may seem strange at first but you'll soon realize that the motion is more natural. On top of that, the heart rate monitor will actually work better.