I would guess that you were treated with NTG for the high BP as the ER physician was ruling out any cardiac problems and wanted to bring your BP down quickly not knowing if you were having a cardiac event.
I would ask your Dr. if he feels you need anything to keep on hand at home. Most patients with hypertension are on a regularly scheduled BP medication.
If you have been under extreme stress then perhaps the key is in bringing down your stress level which would help control your BP. I know that is easier said then done.
I wish you the best and good to see you posting here.