FRA - LEJ is about 150NM great circle distance, so they were not cruising at a high level.
@RockShock:
Breath normally and stay calm, keep your seat belt fastened at all times when on your seat.
If masks do not drop, there is no need for masks.
Masks drop automatically at about 14.000 ft cabin altitude or at any time when manually deployed by the pilot. The pilot has a manual deploy switch in the cockpit.
When deployed, masks need to be activated by the passenger by pulling them down to you.
Once activated, oxygen will be produced from a chemical reaction and mixed with normal cabin air while breathing through your mask.
The chemical reaction produces heat and there might be a burning or electrical smell that origins from the chemical reaction and is normal.
There is one oxygen generator supplying oxygen to all masks for one row of seats.
Oxygen supply is available for about 20 minutes and cannot be stopped once it is activated due to the nature of the chemical reaction.