What would happen if our cells would not get oxygen?

The cell uses oxygen in the mitochondria which produces energy, without it the mitochondria makes lactic acid. Lactic acid affects muscles, and causes muscle soreness. That is if the cell is lacking oxygen, if it didn't get oxygen at all i would think that the affects on the body would be more severe.

Any sickness or anything that would potenally effect the body would become more severe.