Hi Laney.
Well done for taking the decision to do this as I know you have the medical phobia, and it's scary and stressful for you. You will be fine.
I'm going to give you a step by step of what happened for me in hospital (sorry if it's TMI but thought it might be helpful as I know you won't have had a lot of medical procedures before).
A nurse took me to a ward with beds and brought the curtain around my bay so we were private. My partner was sitting next to the bed and was with me holding my hand the whole time. I was asked if I wanted a chaperone or if I was happy with it just being my partner (I was fine with that).
I took off my trousers and pants and lay on the bed with a blanket covering me.
The nurse asked me to bring my feet up towards my bottom and let my knees drop to the side.
She put all the pessaries in in one go. It wasn't painful at all, but a little uncomfortable as she had to make sure they were next to the cervix. It was over very quickly (10-15 seconds at a guess).
Then I was asked to stay lying down for about an hour. This is to make sure the pessaries can stay in place long enough to take effect and so that they know you're not having an immediate adverse effects from the medication.
I was brought codeine to take home with me and told to ask for painkillers if I started getting any pain, then I was left alone with a buzzer to press if I needed anything. The nurse checked on me once or twice during the hour to see if I needed anything and to let me know how long I had left. My partner and I chatted during this time. I also had a book to read to pass the time.
I could feel a slight sensation of the pessaries dissolving and got some mild period cramping fairly soon in to it. I also felt very cold and got quite shivery, which is normal, so bring an extra jumper and thick socks with you in case you get this too.
After the hour was up I was allowed up again and was sent home. They told me not to worry if the pessaries seemed to come out again because they would have been in there long enough to take effect already (but actually nothing came out).
I was given a number to ring if I needed to contact them in an emergency and told exactly what to expect when passing the pregnancy. I was also told which symptoms could indicate infection and told what to do if this happened, and how much bleeding is too much and told to go to A&E if this happened or if I was feeling dizzy and/or faint.
They also let me take home the cover I had been lying on (like a big square absorbent disposable pad) in case I had a lot of bleeding in bed at home.
Once home I did get some side affects; a bit of diarrhoea which didn't last very long and felt a bit sicky and had period pains.
I was told that I should expect to bleed and start to pass the pregnancy about 4-6 hours after the pessaries were inserted.
Unfortunately for me the pessaries didn't work, however it does for most women.
I think with regards to packing an over-night bag, the best thing to do would be to pack one but maybe leave it in the car? (Assuming you are being driven there by someone who is staying with you for the appointment). That way if you really need it it's nearby, but you can forget it's there unless you need it.
Try not to feel upset with your body for not wanting to let go of the pregnancy. I've tried to see it as a positive thing that mine didn't want to give up too easily. I'm hoping next time it'll keep protecting the baby just as fiercely, but hopefully the pregnancy will continue to progress and be healthy.
Best of luck. Let us know how it goes.