I had this experience several years ago at the Canyons. I was enjoying the pow on the right side of a run and didn't notice the terrain change and the tracks were all going left. I ended up doing a torpedo into the snow and almost drowned lol.
Everywhere I put my hand down my arm just sank in. Took forever just to even bend to unstrap. My board just sank another 10 inches when trying to pack around me. Took more than 20 mins to get maybe 10 yards.
Definitely stay calm. If my friends weren't within yelling distance adn them stopping I probably would've freaked and been there for days. It was like trying to do cardio in syrup. Even lying on my board with a buddy using a ski pole took a while.
I was wondering why so many people riding that day had shovels and poles sticking out of their packs....