Is it normal to walk into a store, want to get something, but just walk out instead?

I feel like people are crowding in on my personal space, even when they are not and I am always worried that I'm in someone's way which makes me feel like I have to rush which makes me more anxious and then I end up picking the wrong present and going around and around in circles because I can't find what I want and I wanted to make buy cards and now my peas are melting and I planned to only spend €50, but I've already got€70 of presents and I still haven't found the thing I wanted and will I have enough?
And then when I finally go to check out, I feel like the cashier is silently judging me. Like "Cards? Really? Who do you have to give cards to? And do you think they will like your present?"
Most times, I walk out after walking around in circles and walking into people, but today my brother shook my shoulders and told me not to worry, that he was there and wouldn't let anything happen to me and I felt brave.