Earth's Embrace

Earth and stone rise from the ground, encasing you in a rejuvenating cocoon imbued with earth spirits. You become invulnerable (immune to all damage) and incapacitated. While in this state, you must use all of your remaining hit dice at a 2 to 1 ratio, rounded up. After the cocoon collapses, all healing you receive is halved until you take a short rest.