[crikli]

> What problems specifically?

All aircraft have a VNE speed, the NE standing for "never exceed." Going beyond this threshold invites structural failure and loss of control.

> If you're inside the plane, how does it feel when the plane has stalled?

I've mentioned this in another comment, but the body is a horrible judge of spatial reference. How the body is going to feel during a stall is tough to predict, particularly given that as a passenger a) you will have no visual reference and b) you will be at a unique distance from the aircraft's center of gravity.

That said, you might feel a little buffeting as the wing reaches a critical angle of attack, but once the plane is in a full stall you probably wouldn't feel a whole lot. It's impossible to overstate just how much the body relies on the Mark One Eyeball to properly interpret the sensation motion, gravity, centrifugal force, etc.

[lutorm]

Not all planes are stable in a full stall, some lose longitudinal stability and will be almost impossible to keep level.

[crikli]

Oh sure but most passenger planes are pretty docile a stall.