If you don't feel comfortable wearing the dress don't buy it. As you will get it home and it will stay in the wardrobe... and never see the light of day. If you do wear it you will feel self-concious...
i know what you mean some days im quite happy to go shopping and other days for no reason at all i cant stand it people anoy me i want to hit them if they get to close or bump in to me and usually i feel like just going and sitting in a corner