Spell Slot Recovery, Blood

I'm thinking of implementing this new rule for ALL spell casters (though each class may justify it in different ways)...

SPELL SLOT RECOVERY... without a long rest...

At any point, if a spell caster desires to recoup a (previously spent) spell slot, they may pay for it in blood.
As a BONUS ACTION, a spell caster may regain a slot of any level they have access to, in exchange for a randomly determined number of hit points in damage. This simulates the taxing nature of spell casting, with wizards, sorcerers and bards literally spilling their own blood, and others giving a portion of their life force to their gods or patrons (or even nature itself).
Each individual spell slot regained damages the caster. Additionally, each level of spell slot desired requires an increasing amount of damage to achieve.
You may not use this ability to gain spell slots of a level for which you do not have access, and you may never have more unspent spell slots than your normal limit.
Here's the cost breakdown...

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SPELL SLOT LEVEL / HIT POINT COST*/ CON Save DC (Optional)

*(per individual slot recovered)
Level One / 1d6 Hit Points Lost / DC 10
Level Two / 2d6 Hit Points Lost / DC 11
Level Three / 3d6 Hit Points Lost / DC 12
Level Four / 4d8 Hit Points Lost / DC 13
Level Five / 5d8 Hit Points Lost / DC 14
Level Six / 6d10 Hit Points Lost / DC 15
Level Seven / 7d10 Hit Points Lost / DC 16
Level Eight / 8d12 Hit Points Lost / DC 17
Level Nine / 9d20 Hit Points Lost / DC 18

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You may repeat this process for additional spell slots, as desired. The only limit is when your character either falls unconscious, or fails their associated CON Save. If your blood cost not only drops you (by reaching 0 HP), but exceeds your HP max in additional damage, you die (just as with regular damage).
Keep in mind, this system does not replace the effects of a long (or short) rest, but is intended to work in addition to the existing system of spell slot recovery.

OPTIONAL RULE

If this feels too unbalancing, you can require the spell caster to make a Constitution Saving Throw each time they attempt to regain a slot in this manner (or perhaps beginning with the 2nd time they attempt to use it). As long as they continue to pass their checks, they may continue using this ability. The first time they fail the check, they may not attempt it again until they take a long or short rest.
Further, the DC begins at 10, and increases along with the spell slot level. The table above indicates suggested DCs per spell slot level.
Finally, if you FAIL your CON Save, you do not roll to lose hit points. You do, however, "use up" your bonus action.

Optionally...

If you fail your CON Save you either take half damage OR suffer one level of exhaustion (in addition to the loss of your bonus action for the round). I like the notion of allowing the player decide which detrimental effect to apply, however it may be decided by the DM, depending on your own house rules.

INTENT

Beyond giving spell casters more to do when they run out of slots, this ability also (hopefully) highlights the messy and dangerous aspect of the arcane (and divine) arts. I want magic to be more perilous, while also more attractive to those with a certain degree of "arcane greed" in their eyes.
NEXT UP for experimentation... making spell ingredients more interesting and integral to actual game play!