While you're correct that the phrase, "I got up on the wrong side of the bed" sometimes can refer to a mental state rather than a physical state, I would not consider it odd for an English-speaking American to use that phrase to refer to poor sleeping posture assuming the pain from the poor posture was only a slight discomfort. For more severe soreness, I'd use another phrase. However, another way to express this sentiment that's common near me is to follow the following conversation: 1: "I didn't sleep well last night." 2: "Why not?" 1: "I slept in a strange position and my [back/neck/arm/leg] hurts now." And, probably most commonly that I've heard in the Northeastern United States is to just say: "I slept weird last night and now my [body part] hurts." The use of "weird" instead of "weirdly" in this example is grammatically incorrect, but that is how a native English speaker from America would say it. Saying "I slept [strangely/oddly/weirdly]..." would also work just as well, but, in a normal, informal conversion in the United States it could seem overly formal. Oddly enough, saying this phrase with poor grammar is more useful that saying it correctly in the United States

The best way to express it is "I didn't sleep well" "I woke up on the wrong side of the bed" or "they woke up on the wrong side of the bed" is referring to someone in a bad/grouchie mood.

Hi Tae. I agree with your follow up message: 'getting up on the wrong side of the bed' is more about one's emotions than physical pain. I think we tend to just use literal expressions to describe physical pain, e.g. 'I woke up with achy/sore muscles this morning' And to explain that the pain is due to sleeping with poor posture we might say "I think I slept funny last night" (in this expression 'funny' functions as an adverb, even though it's normally an adjective)