Occupation health is pretty much what it says on the SKA. As a new starter at the hospital you'll most likely have to (or indeed already have) fill in a form about past illnesses etc... and this is just the follow up appointment. So if say you've a history of migraine or back problems they might ask what triggers them. As far as I know it's not just hospitals either, I'm fairly sure it's standard practice.
It's so that you they can ensure you're fit and healthy enough to carry out your placement and that if you do have any health needs they can be addressed so that you're working safely.
You don't say what you're doing in the hospital so I'm guessing it's clinical so you depending on what it is you may also need hep B injection... possibly. I'm not so sure on the clinical requirements for placements.