Check the emergency stop button as not been pressed in you can check this by turning it,
It could be the handset you can override the handset by using the emergency raise and lower on most of the hoists you can do this with a pen tip in 2 small holes below the stop button.
This is normal with this type of mattress , most pressure relieving air mattress go through a 10 min cycle when all the odd cells go soft then all the even cells go soft, when there is cells soft next to each you must get it repaired .
On the actuator, the part that raisers and lowers the hoist there is a emergency lower on that you must pull that up. If it still does not lower get someone else to push down on the boom at the same time it should then go down.