I understand your worries, you are not being silly at all!
are you able to ask friends (school mums) to be on call in the day to pick up your son at short notice/ collect from school if must?
when I was heavily pregnant, then overdue with my DD (1 today!!!) I did organize a daily plan with friends and family to figure out who could "cover" childcare, it put my mind to ease.
If you can roughly sort this you'll feel better prepared, but if not and no-one is available to look after DS, you just have to take him with you to the hospital!
midwives won't be happy, but what else can you do? we had to take DS5 coz MIL got stuck in traffic!
I just want to send you a big hug, it is so difficult coming nearer to giving birth!
there's no way of knowing what will happen, the reason we all worry about the whole thing!
I think you should really talk to your midwife about your anxieties about pain relief and other details, I'm not sure how I could reassure you.
keep talking, I'm happy to "hold your hand" !