I'm having trouble sleeping. Are there any stories in the Sai Satcharita about Udi helping with insomnia?

Yes, Chapter 33 of the Shri Sai Satcharita provides two powerful examples of Udi curing sleep-related issues, as recorded in a footnote by R. Hari Sitaram Dixit. In one instance, a friend of Dixit's had been unable to sleep for eight days, and doctor's medicine provided no benefit. After Dixit gave him Baba's Udi, the friend reported that he slept very well through the entire night after taking it just once. In another case, a friend's child from Bandra had not been able to sleep for two months. The father took the child for Sai Baba's Darshan in Shirdi, and that very night, the child got sleep and continued to sleep well from then on.