I was so sorry to read of your husband's death in another forum.
I believe you said he had heart disease. It does sound like he was having some major issues if he was taking so many of the NTG tabs.
Dizziness, lightheadedness, or fainting when sitting up or standing; flushing of face and neck; headache; nausea and vomiting can be the most common side effects of NTG.
I know this is a difficult time for you and you so badly want to know why he died. This is part of the grieving process so please know it is normal for you to feel this way ~ searching for the cause of his death.
Blessings to you,