Insomnia is common if you are not reaching the minimum guideline intake and/or if you are clamping down (restricting) when it comes to extreme hunger.
Either struggling to get to sleep or finding you are waking up and unable to get back to sleep are often indicators, when you are recovering from a restrictive eating disorder, of hunger.
As you up your daily intake you are liable to find your anxiety about food is ratcheting up as well. Restrictive eating disorders are inherently the misidentification of food as a threat (a somewhat awkward way of trying to explain what is happening in the emotional centers of your brain). As a result you may be treating the minimum guidelines as your maximum and preventing your body from receiving the energy levels it actually requires during the recovery process.
Respond to insomnia with more food: up your daily intake until you find you are able to fall asleep and stay asleep, and if you find you are awake in the night, then get up and have a substantial snack (followed by upping the intake the next day).
Keep in mind that extreme hunger will take you far beyond minimum guideline intakes and that is normal and desired. Please read:
As you re-feed you are going to likely experience a heightened level of anxiety precisely because you are eating food rather than avoiding it. To alleviate this agitation somewhat, consider applying relaxation exercises, meditation and very slow yoga stretches throughout the day to help lower your stress levels and make sleep a bit easier to bring on as well.