Why is mommy so tired?

Last night was the first time Stryker slept through the night, entirely! We put him to sleep after CMMA around 9:30pm & he didn't wake up until 5:15am. So why am I so tired this morning? I've been accustomed to about 3-4 hrs of sleep at a time; therefore, my internal clock kept waking me to check on him. Maybe, this is the start of something new.