Honestly, my buddy had the same thing happen with a "bed" that was basically a bamboo mat on plywood. Woke up every morning with his neck stuck at this weird angle. He spent half his vacation budget on one of those fancy massage places just to function. Tbh it kinda ruined his whole trip because he was just sore and grumpy the whole time.
I get how a bad bed like that bamboo mat on plywood can mess you up. But on my last trip, I slept on a really firm futon that killed my back. I just did some stretches in the morning and used a rolled-up towel as extra support. It wasn't perfect, but I still had a great time exploring and trying new food.