Hi lectro,

unless the camera is hit by an object, falls to the ground or is exposed to other physical damage, the stabilisation system should not be damaged.
You can find more information on our support page.

Sony Europe

Question 1:
Regardless of which system is used, today's cameras are all absolutely robust enough to withstand such armchairs without damage.
Question 2:
Electronic stabilisers are usually only used with small sensors. Conventional stabilisers are better for larger sensors (APS-C / full-frame).

There are different types of systems. Some lock the stabiliser and some do not.
Basically just switch it off when you're going downhill. A parcel is also shaken quite a bit when being delivered by post. :)