Anxiety Support Group
Anxiety is a physical condition marked by intense and persistent feelings of distress, fear, angst or dread. General anxiety caused by routine day-to-day stresses usually passes quickly and is experienced by almost everyone at one time or another. However, such feelings that linger over time and are very difficult to cope with, and which lack a clear cause, may indicate...
You can let friend know "Thank you so much for inviting me to your wedding. I would love to be there but I've already committed to helping my pregnant sister move that day. I hope it goes well for you and I wish you the very best." And if you can and you want to, send them a gift for roughly the same value as the gift they gave you.
And if you don't like someone - or they don't like you - it's not worth trying to keep up appearances unless you absolutely have to (your bosses wife for example).
The thing is, it's a wedding, so the bride and everyone there will be wrapped up in the event and they won't think about the people who weren't able to be there. But if you do go, it sounds like you'll have a miserable time. So what's more important, taking care of yourself and helping your sister in her time of need or pleasing someone who doesn't like you and probably won't notice your absence anyway?