Unfortunately, not, but I can relate. My wife has hyperphantasia and sometimes struggles with vivid dreams and memories. She says she sometimes wishes she had aphantasia like me. Most of the time, my dreams are nothing but blackness. The only sense that I can truly remember/imagine are sounds and even then, it usually takes a lot of repetition before it sticks. He could try something I use to mentally reset my brain: Controlled breathing. Inhale for a count of 4, hold for a count of 16, exhale for a count of 8. Repeat a few times, as necessary. I've found that this can completely break a train of unwanted thoughts, at least for me.