Apple charger port magnet has lost it's pull
That internal MagSafe port is fairly inexpensive and rapid to exchange. The likelihood is that either part of the internal magnet has shifted or the entire unit has moved internally.

If the magnets inside are loose they could short a more expensive part or be a fire hazard. Best to get it in the shop. 

The strong rare earth magnets won't demagnetize from a physical shock so it's likely there is internal dislocation or damage.