I started at 40mg some years ago; I did indeed feel superhuman, but my sleep suffered periodically and I had some other side effects -- morning nausea sometimes, especially when combined with coffee.

I found ways to cope: reduce coffee intake, have some plain yogurt in the morning, as the protein seems to help buffer the stomach, medicate early in the morning (6:30am) and exercise hard after work to promote better sleep. Still, it was a drag, and too easy to miss a beat in my routine.

I had to quit taking Strattera for two years while attempting to become a pilot, but it turns out the FAA hates ADHD kids and once that fell through, I resumed at a much lower dosage of 25mg. While I don't feel quite as capable at the lower dose, the side effects are significantly more mild and I generally don't notice them. I still make sure to medicate no later than 7am, as a precaution, but there's no correlation between being medicated and having poor sleep.

TL;DR stick with it for a few days and don't hesitate to ask for a lower dose if you can't hack it. The drug does a world of good for me, and it promotes habits that persist even when I go unmedicated for awhile (e.g. on weekends and often while on vacation).