mood crashing quick

Hey
Just wanted to see anyones thoughts. I been on sertraline for clin.Dep for over a yr, the depression prob have had like 15 yrs. I was having a pretty good day with friends today having a laugh & as we were leaving where we at, started to get really anxious & feeling overwhelmed that I needed to get home. Got my usual Saturday lunch from shop with friends (e.d. issues so I have same every Saturday) we sat eating & I still felt really anxious, jumpy & like I really needed to get home. Scratched my hand so much it was bleeding.
I didn't wanna be rude to my friends, b4 I was on meds we had a rocky time. But it was odd & freaked me out my mood just dipped so quick & I felt so alone even tho I was with friends & like I just wanted to curl up somewhere safe.
Sox for rambling it just freaked me out & I hate myself for getting like that.x