Ours did the same but 9/10 times it would inflate back to proper height. After seeing the condition of the rubber on both sides I decided to swap them anyway as even if it they weren't the problem they soon would be.

My biggest question was why both sides were drooping. Having both springs fail at once sounded like an unlikely coincidence. As it turned out, only one was bad and the sway bar was pulling the other side down. This effect may be greater on cars like mine with Sport Suspension.

All of this became completely obvious when I simply jacked the car up. At this point I already had the new air springs and was going to change both, and I knew this was going to be a lot easier if they were already deflated, so I removed the fuse for the compressor and drove it for about a mile until it was completely dropped in the back.

When I jacked up the back, this is what the bags looked like:





At that point you just turn them about 1/8 turn and they practically fall out.

I too contemplated going to standard springs but I like to keep my car OEM and what finally swayed me was my local auto parts store sold Arnott air springs that come with a lifetime warranty. They were the same price as OEM but with the warranty. As easy as they were to replace if I have to swap them every 5 years I'm cool with that.