What can I expect them to do to my happiness?
Depends if you like the job, it could go the way will wrote. Or something different. You may not get to sleep during the day, thus be miserable at night because of sans sleep.
Will my social life suffer?
If you like to go out and socialize in the evenings, then yes. It will affect your social life. Because (if you are on a 4 on, 4 off rota for example) your days off could be different to that of friends days off.
What are your shift patterns anyway??.
Will I become a vampire?
There is a chance, but it is a slim one to be honest.
My opinion of night shifts. The pay is excellent, but it isn't compensation to what it can do to you physically and mentally. You'll probably have no time to do anything outside of working days, then the first day off as such from work will be bad. Unless you stay up all day instead of sleeping, then sleep at night. Leaves you 3 nights of social, or 4 if you decide to nap.
If and when you decide to leave work, it will take time to get back into a routine of "normality".