When you put on armor pieces that are supposed to subtract 19 heath from your health bar, only 18 health is actually subtracted. The only way to update it is with an instant health potion or by being hit, however, trying to give instant health through a command will make it seem like you've died without you actually dying. Pressing the respawn button will put you exactly where you were before but your body will be red, slanted, and glitching out.