D&D 5E (2014) Are Sorcerers' and Warlocks' Spell Slots Backwards???

[DND_Reborn]

every casting should cost you some amount of physical energy - hit points, levels of exhaustion, movement speed, Constitution points, or something similar.

My groups have considered many such alternatives--based on the SW d20 game, where Force-Users had to spend Vitality (i.e. hit points) to use their Force Powers.

So, the idea of spending hit points (1 hp/ spell level) has been considered a lot at our tables...