Medicguyette welcome to Neurotalk,

spontaneously vomitting is not a common symptom of PCS as far as i know.
You mention a stabbing feeling behind your eyes, do you also have visual disturbances as well? Especially when standing up suddenly or coughing?

Sometimes vomitting, combined with visual distubances is indicative of increased intracranial pressure. The increase in pressure can activate part of the brain called "Area postrema" inducing vomiting, while also putting pressure on the optic disc causing visual disturbances. Usually though, people get progressively worse if they have this condition and don't feel better till it is resolved.

This is only a suggestion, so don't be alarmed


-GlassHead