I was in Creative and then I switched into adventure and I couldn't see my health in the top left corner. So I asked my friend to hit me with a wooden sword and I died straight away.

I was in a 2-player flat world with my friend. He and I were building a parkour mini game map. I had just finished building Level 11 and I wanted to try it out so I switched into Adventure mode and I noticed that my health (hearts in the top left corner) wasn't there. It had just DISAPPEARED! Gone! So my friend teleported to me and I asked him to hit me once with his wooden sword and I died straight away! I think, WHAT'S GOING ON?!!!! So I continuously switched to and fro adventure and creative. Then I tried survival mode and the same bug was there! So i'd like to know what is going on and how I fix it.