If you do some sort of exertion, your heart rate will jump from the average 60-80 bpm, to around 140 in a matter of seconds.
going down fairly fast is normal as well.
But 162 after walking, i'm not so sure about (there is little difference in heart rates whilst exercising between the fit and unfit, only large difference is in resting heart rate and recovery time)
Yes with a heart rate of 120 you should be dead...