Any concern to be had from using a riding mower regularly?
 

Would the bounces that typically occur when mowing and going over bumps at the frequency in which they occur (probably around 20-50 per lawn) be any concern from a sub-concussive standpoint? I try to mitigate the force going to my head by leaning forward and going slowly, but I still feel it is possible in the numbers they occur that it could be an issue. But it also seems unlikely that the force exerted is anything significant given my body should be taking the brunt of it. Just wanting to make sure I don't regret mowing so much later on.

Not a problem at all......Now the vibration and the noise did bother me, but by all means never made anything worse.

No, those rough lawn bump don't come close to a subconcussive force. I have frost heaves all through my lawn. I do my rough lawn every week. The forces are mitigated by pneumatic tires, springs under the seat, foam in the seat and the butt and back absorbing the force. Even if there was no mitigation by the tractor, the forces are just not enough.