One thing I learned (the hard way) is to make yourself a morning person before you make plans to workout in the am. I used to have the same anxiety about not being able to fall asleep if I had a workout early in the am. Mostly because I knew I didn't like getting up and wasn't rational in thinking I'd do the workout later so I'd go back to sleep. Then I'd be mad at myself all day and feel like I'd failed at something before I got out of bed. It was a downward spiral that led to me being anxious about being anxious. Meditation before/as I was going to bed helped me fall asleep and I just didn't plan any am workouts until I was a month into being a morning person (a lot of coffee helped that)!