it depends. almost all the night-time cold medicines contain medications that can make you drowsy. adding a benzodiazepine to that could make someone excessively drowsy. without more specific information about which medications you are referring to i would have to refer you to your personal pharmacist. he/she has your personal medical information and can help you best.
is it ok to take a benzodiazepine after a dose of over-the-counter night-time cold medicine?