Nitroglycerine is a powerful vasodilator. Anyone who has been treated for a heart attack will tell you that the nitroglycerine administered to increase cardiac vessel blood flow will give you a whopping, fierce headache. Some cardiologists even administer morphine to ease the headache pain.
If you have ever worked in a mine where they use it to blast(I have, a gold mine back in the 1960s)you will also know the fumes caused by the explosion will also you give you a headache, a bad one. You have to let the fumes clear before you can go back in after the blast. Sometimes we would wait until the next day to go in.