I had some diazepam (2mg) about 4 hours ago to help with a panic attack. when would it be ok to have some more, just to help me relax a bit?

Consult prescriber: Your prescriber would know you & your clinical situation to guide doing. Generally, diazepam is dosed as 2-10 mg 2-4 times a day & best reserved for severe anxiety. It may be habit-forming & abrupt withdrawal after steady use may have unconfortable effects. To relax a bit it is best to learn anxiety mx strategies like those in "the relaxation & stress reduction workbook" by davis & mckay.