Change of Plans (Vent)

Hi Guys. Just wanted to do a little vent/ramble as I'm freaking out. I just dropped my partner off with our 2 kids (who are 5 and 2) at a Christmas party around one of her friends from work's house. We had agreed I'd go shopping for a few bits that we need to take to my Mum's later for a Sunday dinner. I had it in my head that I'd drop them off, go to the shops, then pop home for half an hour before picking them up and going to Mum's. My partner dropped in conversation about 30 mins before were leaving that she thought id be joining the party straight after shopping. As soon as she said this i started to get the signature, anxious, hot face and twitchy stomach feeling. Couldn't think properly the whole time up until I dropped them off and could feel I had a really short temper so was trying not to snap at the kids. She said when I was dropping them off that I could go home if I wanted, and I will, but I feel guilty now and obviously itll take anywhere hour or two for this anxious feeling to subside. I just kind of wanted to vent somewhere where ai assume people understand. Im not even sure Ill mention to my partner when I pick them up that this was my reaction (I hid it as much as possible) but I feel like I should share with my partner than I burst into tears as soon as they'd gone? Especially now I've been diagnosed. I dont like burdening her with this stuff though. Anyway, thanks for reading haha.