FRIENDSHIP PROBLEM PLEASE HELP!?

So when i was about 6 or 7 i had this best friend called hannah- I took her camping,i went to her house all the time,we went to the circus together after i was 6/7 we just stopped being friends and i wasn't bothered because i had made new friends, after primary school we went to the same secondary school but we werent friends with the same people and she ended up moving to sweeden at the end of yr7 the first year of secondary school I am in yr9 now so i am 13,i've made so many new friends and completey changed friendship groups and have completely changed as a person-I've never thought any thing of our friendship until the past few weeks when i have been thinking about my childhood and i started remembering that i was really good friends with her, and it makes me sick to my stomach,i get so anxious when i think about our friendship and feel like i am going to vomit,even though we haven't been friends for a good 5 years but whenever i think about the times where we would hang out together i just hate it i have no clue why, i never thought about our friendship in a bad way or any way until now and thinking about it makes me have panic attacks, and when i see old photos,i feel like people wont want to be friends with me if because i used to be friends with her, which sounds so crazy or like i cant have a really cool group of friends because i was friends with her, i also feel like i wasted a major part in my life being friends with her-Can anyone explain why?