I tried lucid dreaming but my arms swung involuntarily.?

I tried lucid dreaming, by remaining fully relaxing and laying on my back in the corpse position, (and yes there was some sound, a tv, but I couldn't help it so I just tuned it out) but about 10 minutes in my arm involuntarily swung and hit me in the face. Immediately after I saw a shadow that dissipated quickly. I then ignored it and tried a second time. That time, my arms swung up into the position people are put in when they're in coffins. That time I stopped trying and haven't been able to go back to sleep after 35 minutes. Ever since I've had insane goosebumps and have been completely paranoid, and it may all have been in my mind, but should I be concerned?