PENKO, my answer in post 63 was for you. If in manual flight (Boeing) and not spooling up the engines EARLY, when leveling off (and with less than 60 seconds idle time) - you are setting yourself up for troubles, i.e. a serious under speed condition.
If you e.g. keep the throttles closed and aggressively pitch up to stop the descent (passengers and flight attendant won't be happy). and THEN reapply thrust. AFDS doesn't do it that way. It goes into ALT ACQ and slowly reapply thrust and slowly increase pitch, so that everything comes together simultaneously (holding altitude, having correct speed and thrust).
If you are lucky (as most times during the descent you are light), you will still have a big speed range to absorb the under speed, if you have to descent for traffic while still heavy, you are worst case setting yourself up for a stall recovery or and embarrassing request to continue the descent.