Hi there,
If I was you I would definitely check with family if they've had pethidine and what their reaction was.
I had it with my first, pushed into it by midwives, and passed out pretty much straight away. Came round each time there was a contraction, but didn't know where I was, what I was doing, or even who i was, and promptly passed out again when the contraction finished. DS got stuck, I'm convinced because I wasn't pushing because of the pethidine, and had to have ventouse which seemed to last forever according to DH. He says the doctor literally had her feet against the end of the bed bracing herself to pull DS out. After the birth DS was rushed off in distress, DH thought I was going to bleed to death and I couldn't walk for days. Not a good experience for any of us.
Afterwards told my mum about it and she said she'd had pethidine with me and exactly the same thing happened to her so she didn't take it with my brother.
For DD my birth plan basically said no pethidine on every line, and I was terrified that I might have a reaction to anything else so very wary of them too. My local hospital has a new a very good midwife led home from home unit with private rooms and birthing pools and anything else you might want apart from drugs (gas and air only). I went in there, had a water birth, and one shot of gas and air when she crowned and I panicked (basically the midwife got DH to shove the mouthpiece in when I decided I couldn't do it after all) but apart from that nothing. And it was so lovely compared to the first time. DH says it's not surprising, considering I didn't have someone shoving a plunger inside me for more than an hour
Everyone's different but do check about family just in case. Midwives can try to push you into pethidine when you're not in a state to make a rational decision, probably because it makes you more docile and easier to handle .
Good luck with it whatever you decide, it'll be great. After all, it's such a short time compared to the rest of their lives