Blood Offering

You cut yourself and offer your blood to a higher power in exchange for magical energy regaining an expended spell slot of 5th level or lower. You take an amount of damage equivalent to 5 times the level of the spell slot regained and your number of maximum hit points is reduced by the amount of damage taken until you next finish a long rest, even if you have the inured to undeath feature. If your hit points are reduced to 0 this way, then your hit points are instead reduced to 1 and you cannot cast spells until you next finish a long rest.

If you use this spell to regain an expended spell slot multiple times before finishing a long rest, the amount of damage you take from using it is increased by 5 for each time you've previously used the spell.