Is this a meltdown??

Hey everyone 

Sorry to toss this out there but wondering if the following constitutes as a meltdown? 
I was with friends for dinner on Sunday and felt like I had to endure into the evening (probably 12pm)

I felt ok Monday and Tuesday but I feel dreadful now. We were invited to their 40th birthday this coming November while we were at dinner and I can’t stop going over this even though it’s months away. Obviously this is a big thing for me and my brain is trying to pre think scenarios and generally how I’m going to get through it. 
The whole evening was exhausting and I was very quiet, I just wanted to go home. I put myself through this for my family tbh as I don’t want them to miss out.

I really feel quite low today and the slightest thing makes me panic. 

Would be very grateful if anyone has any thoughts please?