ramdomly i lost most of my hearts while towering in the nether randomly.

I was working on a tunnel project connecting two houses. there was some water I put in the tunnel. later I was towering up in the nether getting glow stone and I lost most of my hearts. I deleted the video but I experienced random damage. No fall damage no nothing. One thing I would like to point out is that when it happened I saw bubbles and then I lost my health. I think it happened to me before also. The video was 180mb so i doubt it will upload the video anyways.