Jekyll and Hyde

I wonder if Robert Louis Stevenson had a toddler when he wrote Jekyll and Hyde. I sometimes feel like I am living with my own 3 year old version of the affliction--the difference being that I am well aware of the reasons and cure for the child-sized version. For the past month or two, Sarah has been my own personal version of Jekyll & Hyde. She will wake up one morning in hysterics, ornery as an old mule, and acting like a spoiled baby (and I really don't believe in spoiling my kids), then the next morning she will be a sweet little angel; giggling, helpful, and sweet as sugar, Sugar. In fact, some days she will even go around singing "Sugar, Sugar."
The difference?
SLEEP!
And I'm not talking about hours difference. Two minutes of sleep could mean the difference between Jekyll and Hyde at our house. If I accidentally wake Sarah up when I am getting the older girls up, I can rest assured it is going to be a LONG day. Sarah hasn't taken a regular nap for about 2 years, and she hasn't had an accidental nap in over a year.I have tried, unsuccessfully, to figure out a way to get her to take one--especially when it is desperately needed.
However, some mornings (like today), she will wake up all on her own and she is a little ray of sunshine.
Right now it is pretty funny to see the sleep-deprived split personality, but I am hoping that by the time she starts kindergarten it will have cured itself.
Otherwise, I will have to petition the district for a medical release on days when she is exhibiting symptoms of Hyditis.