12 year-old boy's difficulty falling asleep - anxiety & fears

Our 12 year-old son (just finished 6th grade), who has always been happy and healthy has started having a lot of difficulty falling asleep at night. He is awake until 11 or 12, even 1am some nights unable to sleep. He is tired during the day, to the point of not being able to focus in class. He often comes home so tired from school that he gets in bed at 3:30 pm and just rests. He doesn't nap in the afternoons, says he can't sleep then either. After about a month, he finally confided to me that he is having a terrible fear at night that his heart is going to stop. He thinks about it at night and when the thought comes, he can't get it out of his mind. Sometimes he has the fear during the day but can usually distract himself by activities. We have tried a bunch of relaxation techniques and other sleep hygiene exercises that don't seem to help. If I lay next to him for an hour or so and reassure him, he can often fall asleep easier but not always.

We don't know of any trauma or event that might have triggered this. I have asked him about issues at school and he truly seems like everything is fine. But I know middle school is always a challenge and perhaps there are things happening that he isn't sharing with us, although he always denies that anything is wrong or stressful.

A colleague who is a psychologist recommended cognitive behavioral therapy and/or biofeedback therapy. Does anyone have any recommendations for a provider of those modalities who is good with "tweens"/teens? I have done some preliminary searching but would love some concrete recommendations. Any other ideas from the community are welcome also.  Thanks in advance!