I just noticed a recent change of sleeping pattern of my 2nd son, who is now 1 year and 3 month old. To be accurate the change started about 1 week ago.
Before that he used to turn in right away after being fed with 6 oz milk, around 7:30pm, and wake up around 2am for more milk and fall back sleep immediately. If we feed him with water rather than milk out of concern of overfeeding, he would groan in complaints, kicking his feet for 30 minutes but eventually manage to fall asleep again.
Gone were those days. Starting last weekend he refused to sleep after taking the milk at 7:45pm. He refused to stay in his cradle, he was very adamant and keeping motioning me to take him out. After I complied he would happily stumble around with my support under his arms, or play a ball, engaging in all activities but sleep. This could last for hours. Like today, he didn't fall asleep until 10:48pm. He still wakes up at 2 or 3am, but now it takes almost two hours before he sleeps again.
My son seems entering a new phase of development. He just starts learning to walk and speak, yet his mind matures at a faster pace. He starts demanding and his demands are simple yet clear and he refuses to take a "No" for an answer, otherwise he would cry at the top of lungs (in one occasion he cried so hard that he uncontrollably threw up). To me he seems tired of being a good boy, or my father's tough gene skipped my generation and passed onto him. :-)
To be serious, what just happened to my son? Why did he become so intolerant all of a sudden? The only circumstantial change is that his mother went on a business trip. But even when she was home, I spent equal amount of time (if not more) with my son and he didn't seem to be affected by his mother's temporary departure. (my wife had a few business trips before)