Impact of praying fajr on sleep continuity

As more and more studies establish the importance of sleep, and specially of continuous sleep, I am wondering how does praying fajr impact sleep. I recently started praying fajr, and I am finding that due to split sleep, I am not as refreshed as I used to be when I used to sleep continuously. I live in North America where time duration between Isha and Fajr is only 3.5 hours during summer months. Therefore, sleeping early is not an option. I dont want to miss fajr either. If someone has found the right balance of sleep and prayer, then I would love to know. Thanks!!