When you lose health and have he instant health effect, you 'die' but don't die so your screen goes sideways.
Steps:
1. type in a command for an extended instant health. (Ex.: /effect @p minecraft:instant_health 999999 4)
2.give yourself an equipment that gives you player extra health. (Ex.: /give @p diamond_helmet 1 0 {AttributeModifiers:[

{AttributeName:"generic.maxHealth",Name:"generic.maxHealth",Amount:9999999,Operation:0,UUIDMost:35617,UUIDLeast:83126}

]} )
3.go into your inventory.
4. repeatedly take off and put on the equipment
5.you should now be sideways in your inventory.