You will be ok OP. I've been seen in a few cardiology clinics now and there really is limited cause for concern. Unless they suspect something serious having done your initial ECG they are unlikely to do many other tests on the day and will book you in at a later date for them if they feel they are required. This is especially true if you are young, have a decent BMI and no existing health issues.
Likely you will wait a while (take a book etc) in the waiting room, be called in to see the nurse who will take some details and to an ECG for the consultant, take your height and weight and send you back to the waiting room and then you'll go in to see him or her. You can bring your partner for whatever you like.
The consultant will then discuss your symptoms, a medical history, family history, any medication you take, may consume checks such as listen to the chest, take a pulse etc. You can ask any questions you like and he/she will advise what they want to look into next. Usually any further tests are to rule things out and error on the side of caution. Yes it is likely that they may take bloods, your GP results may not be on the system and there might be other things they'll want to look for to rule them out. You usually get sent down for bloods at the end, the consultant will send you down to phlebotomy with your form and they'll deal with it when you get there.
OP I recommend making a list of all your symptoms for the consultant so you can give them it, take any medication you are taking with you too.
With regards your 'funny turns' OP do you find they are worse when you get up quickly or have been standing up for some time? Worse when you are dehydrated or after a meal or similar? Do the symptoms alleviate when you sit or lie down? Has anyone taken a sitting to standing BP result?
There are many things it could be OP, very few of them are serious and many of them may mean your heart is perfectly healthy but there is something else going on 