I'm an enthusiastic explorer of the mind-body link. I'm a Hindu by upbringing and a curious inquirer into the nature of things. I'm a control systems engineer currently working in systems biology and was always interested about prana/chi. Recently I had a weird first person experience during the practice of yoga nidra. It's the practice of deeply relaxing but holding clarity and focus of mind simultaneously, in the supine position, and moving the the focus of awareness through different parts of the body one by one.
Mostly I have experienced a sensation of tingling and vague throbbing sensation seemingly correlated with the pulse throb. But I that day the relaxation was particularly strong and I was almost in a hypnagogic state where I felt the "sensation of tingling" coalesce into a narrow region approximately half the width of a finger tip. Sharpness of the sensation was new and almost felt like a clear but mild electric current. It followed my attention and I attempted to move it throw my left arm. It felt as if a charged thin thread was moving through the upper flesh, just beneath the skin, tracing a path that felt like it was already there.
I lost control of the "droplet" near my shoulder and it moved straight into my heart region automatically as if it was slipping towards it creating a sharp but mild pain which startled me out of the relaxation state. The pain was clear and sharp. I tried to recreate this experience but I have not had success in doing so yet. Mainly because of the extent of relaxation without dullness of mind that it seems to require. I have started practicing shamatha (mindfulness of breathing) to get a hang of this. I found Alan Wallace's material on concentration development to be the most erudite and practical. Please do offer suggestions on finding authentic teachers and practitioners in Tai Chi/Qi gong.