Carguk's Lung Collapse

Target one creature with a size of medium or lower you can see within range. A translucent bubble appears around that creatures head. That creature has to succeed on a constitution saving throw or be silenced for the duration. Additionally that creature cannot breath for the duration. At the end of each of the turns of that creature it has to make a constitution saving throw. On 3 failures, roll 5d8. If the total is equal to or higher than the creatures hit points, that creature falls unconscious. 

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, roll an additional 2d8 for each slot level above 3rd.