Need help (Diazepam)?

I'm having a minor operation tomorrow and the Dr has given me 20 mg of diazepam to take due to extreme anxiety. I forgot to ask him whether to take them on an empty stomach and have something to eat first. I read the leaflet that comes with them and it doesn't say anything. Does anyone know, if so please let me know. And if possible, what is the feeling of taking that amount, I usually only take 4mg a day and it helps with my anxiety, but tomorrow I have to have a need in my toe and the Dr says its going to hurt and I'm one of those people who can't stand pain, so what will the tablet do to me. Any answers would be really appreciated. Thank you.