I found this video to be very good with relaxation (good for when you are feeling too amped up but need to go to bed, plus many other situations).
Also to me this illustrates the kind of control that we can learn to exert over our ourselves (and our free agency) once we know about this then we can choose when to apply it. It is not meditation and does not require practice - once you know about it then you can do it.
From the description: "Andrew Huberman reveals a simple breathing exercise that acts as a kill switch for stress. It's called the "physiological sigh" or "cyclic sigh", and it can help you short circuit the stressful response." (video is 11 min. long)
