This may be a warning sign for the onset of more serious altitude illness. Treatment is rest with further ascent recommended only after symptoms have ceased. The only treatment is immediate descent.
Death can come on quickly.
The only treatment is immediate descent. Factor in a rest day every 3,000'. Spend at least one night below 10,000' before ascending higher. If you don't feel good, don't raise sleeping altitude until you feel better. If you don't feel better at the current sleeping altitude, descend to below where you first felt sick.