Newbie Qs on stalls and spins

I've seen that John Denker in his article advocating pilots to keep
practicing recoveries from stalls and spins at a safe altitude...
which prompts me to ask the following:

1. Since I don't think I've experienced a stall or spin before, is it
a nice sensation to experience as a passenger, or wouldn't one be able
to tell?

2. Is it ok for pilots to practice stalls and spins on commercial
passenger aircraft in mid-flight? I ask, since I don't think it's
happened on any flight I've flown so far - unless some pilot did it
without informing the passengers :\

Ramapriya