Hello I was searching this Bc I am dealing with the same thing. I’m 17 and for as long as I remember I’ve had this. It don’t happen when I’m relaxing normally; I have to focus on relaxing deeper and then my legs and feet get this almost like tingly feeling and it’s only my legs and feet and like you I can’t hold it for longer than 10 seconds. I feel like if I do it often it could lead to something and maybe master some crazy mental ability. Everyone I’ve talked to about this thinks I’m dumb crazy or just have no idea what I’m talking about. I’ve never checked my eyes while doing it but I need to know what this is called or means because it’s been a topic I’ve wondered my entire life that I could never relate with anyone else till now. And sometimes when I am doing it for a little I can make my upper body mainly shoulders almost like shake a little.