Dangerously high blood glucose levels ( around 300 ) require emergency medical treatment. Since your husband is already experiencing nausea and vomiting
,you should take him urgently to ER because untreated high sugar levels can cause life threatening dehydration
and loss of consciousness
There is no natural way which can correct high blood sugar levels very fast.
The only way ,in such a situation,is injectable insulin
and proper intravenous fluids.
I hope you understand the gravity of situation.