Ha ha, I love it! Were you also keeping your belly tuned into what day it was? Jk. While I don't subscribe to your child understanding what day to come, I certainly think your body understands that you are ready to relax and that your subconscious has a strong ability to influence your body functions.
As for my own ds, he is strong willed, and sat early right at 4, crawled early at 5, but then walked average just before 12. Looking back, I see how this reflects his temperment more. He is cautious with heights especially, and in physical things ie bike riding, very cautious until he feels confident that he won't fall. He wants to be sure of himself before he tries. Sitting or crawling wouldn't have had that same danger.