I've had this problem for a few years now. Eating outside is extremely difficult for me and I can't figure out why exactly. 

The day when I'm supposed to go eat outside, I plan my whole day around it. When do I have breakfast so I can have lunch early enough? When do I have lunch so I'm hungry when I go to the restaurant? It causes me awful anxiety, and eating becomes so difficult that I feel like even putting food in my mouth makes me gag.

Today I was supposed to go to a restaurant at 6pm. I was nervous the whole day, had tightness in my chest and eventually got a panic attack hours before going. I felt like I couldn't get over it, I was feeling nauseous and eating felt like the last thing I could do. I took propral, had a few glasses of wine and eventually loosened up enough to tell people about my anxiety. In the end I went and managed to eat a chicken salad but it was difficult and I had to take a few breathers. Awful, exhausting and super sad. I wish I was able to enjoy the restaurants with my family and friends.