Yes, have had it a lot. Body heat warms the air in the mattress. When the warm air reaches cold or cooler surface below it condenses.
I tried several things for several years. Insulated pads, plastic sheeting and raising the mattress off the hard surface an inch. Once I raised the mattress I realized I was on the right path. No amount of heat or ventilation helped, until I rasped the mattress. It was still a problem because it was hard to get much air movement under the mattress and I did not like turning on the furnace just to dry the mattress. We then got two mattresses and would tip them up every day. That worked, but were lazy so we got tired of that. Next step, tore out the original bed. Rebuilt an open frame about 20'' off the floor and covered it with expanded metal supported about every 16''.
End of problem plus we gained a lot of very accessible storage space. No more doors to fight with. We just use tote bins that slide in and out. The bins also make it much easier to load and unload. Of coarse it didn't look as nice, but my creative wife said no sweat. She just just got a larger bed spread and lets it come down on the sides. That was a close call in the area of doesn't look nice. Even with the bedspread covering most of the opening the mattresses remain dry. Air space between the mattress and what ever it rests on is the answer. Wow, I could have written that last sentience first and been through with the answer.
Hope this helps, Tom