Blood Shield

You drain some of your life essence to form an invisible barrier of magical force to protect yourself. You take necrotic damage equal to double your proficiency bonus which cannot be reduced in any way, ignoring any temporary hit points you may have, and you reduce your maximum hit points by the same amount. You have a bonus to AC against the triggering attack equal to your proficiency bonus, and you gain resistance against force damage for the triggering attack. The maximum hit points you have lost from casting this spell are recovered after you complete a long rest. If this spell reduces your maximum hit points below one hit point, you will die immediately.