Takeing damage in my world for no reason

When I was playing minecraft bedrock edition on my nintendo switch I was building a house when I was working on the tops of the walls I started to take half a heart of damage so I climb down the ladder I had placed and I stopped taking damage I checked the nearby trees to see if a skeleton  was under a tree after a good 5 mins of looking I didn't find anything other then a flock of sheep so I climb back up again and started taking damage again I do have a world seed if it is needed and I am also  going to update to 1.18 when my switch lets me 

 

 

Update: I have updated to 1.18