My daughter with pku will be two next month and we've had many stressful times where illness or a growth spurt has brought the level up too high or down too low. It is stressful- but so far i've not seen any negative long term consequences. You only can do what you can do. I remind myself of this often. Being stressed about it isn't helpful for anyone- and while it is a science to keep the numbers in range- it is also an art. I find that her being stimulated or getting more excercise or more or less sleep throws the nubmers out too sometimes! you're doing a great job and it will be ok!