What Happens:
When you equip Items with health boost stats(I'm not sure if any of the happens with the other stats) and simultaneously giving them a health boost effect.

Commands used:
A leather cap with health stat boost of 40, the color red and a custom name:

/give @p leather_helmet 1 0 {display:{color:16711937,Name:"Red Hat"},Unbreakable:1,AttributeModifiers:[{AttributeName:"generic.maxHealth",Name:"generic.maxHealth",Amount:40,Operation:0,UUIDLeast:894654,UUIDMost:2872}]}

A Health boost effect for just a few seconds:
/effect @p 6 30 6 true

Attached:
A photo of this weird death state whilst active AND a world built with the setup because I couldn't recreate this it's this exact setup.