Night Nurse contains Promethazine which is a decongestant, I have been advised several times by Consultants to avoid any decongestants.
This is what I can gather from a little research...apparently decongestants can act similarly to adrenaline, thus they can cause blood vessels to constrict, alter the pressure of the fluid in the eye and increase blood pressure. Also, as with adrenaline, decongestants can cause a release glucose into the blood stream from the liver, raise blood glucose, and cause the production of ketones independent of blood glucose level. For most people, it is not a big deal but for diabetics we need to err on the side of caution. If it is a big deal for you, test your blood sugar, take the decongestant, then keep testing to see what happens.