Racing thoughts and physical tension are caused by an overactive sympathetic nervous system (fight or flight). You can't think your way into sleep; you have to shift your biology.
Simple, effective, and guided.
Inhale quietly through the nose for 4 seconds to oxygenate the blood.
Hold the breath for 7 seconds to allow oxygen saturation.
Exhale forcefully through the mouth making a whoosh sound for 8 seconds.