You are completely normal. I hated traveling for business, or even going to my sister's after I found out. I would have panic attacks because the mind is really good at spinning scenarios.
You are so very new to the news. You are going to question everything including yourself. Give yourself some time. You need time to process that you've been cheated on and hurt by the person you thought would be the least likely to do this to you.
You are not being ridiculous at all. Do whatever it is that you need to feel safe. If that means cancelling the trip, then so be it. If that means having your husband check in with you every hour, so be it. You get to define what you need going forward.
ONS or LTA - either way it was cheating. You have to deal with the reality of his horrible choice and look at how you will begin to heal.
Good luck. You can and will make it to the other side.