The few times I road across the ocean , I never got sea sickness. If the time zone changes, I change with the time Zone. May take a day or two for your body to adjust.

Ireland is 4hrs ahead of Philadelphia.
If you take meds at 8am and don't change it, you'll be getting up at 4am to take medication. If you are going for a short trip this may not matter.
If you're going on a long trip, slowly change your medication time to Ireland's time zone... BEFORE you go for your trip. Then once you get there you can just continue on your vacation.
Then do the opposite once you get home. You get back and slowly change your medication time back to a Philadelphia timezone.
Note: If you've never changed your meds before please be careful. Make sure you always double check information about your health (someone could have typed it in wrong).
Have a great trip. Take care.

I have never been overseas, but my guess is that you take your medications the same time your body is used to in the US. If you change your medication times, you put your system out of sink from the normal time of taking your medications. To be sure i would say ask your neurologist. And tell them how long you are going to be away, and what is the time zone. Have a nice trip!