How will diazapam make me feel?

[BirthdayKake]

I've only ever taken it at night to help me sleep after a car crash, but I have a big day coming up and I'm planning on taking one or two in the morning (I won't be driving anywhere!).

What will it do?

Hi. What type of 'big day'? Are you very anxious? What strength are your tablets? You might end up drowsy. Sorry, you need to give a bit more info please.

They're 2mg. It's my wedding and I'm VERY anxious

Congratulations!
I know exactly how you feel, I'm a very anxious / social phobic type. I'd take one the night before. See how you feel in the morning, and perhaps take half. Take one with you, and just knowing you've got it there will reassure you.
But first have a dry run. Pick a day when you're not doing much, take a tablet and then you'll know how it makes you feel. If you're not used to taking diazepam you run the risk of feeling drowsy/ sleepy/ spaced-out/ not with it.
It's definitely a very bad idea to drink alcohol with diazepam. Are you intending on drinking? If so, do not take the diazepam.
Have you tried propranolol? They are beta blockers. They are non sedative but stop the physical effects of anxiety (shaking, palpitations, dry mouth or whatever your symptoms are). If I were you, I'd go to the doctors and ask about them. I've taken them for exams and interviews, they're very good, and doctors prescribe them quite freely as they have very few side effects (unlike diazepam).
Hope this has been of help!