I wonder if this is a feature of autism that many people experience, a wide and often sudden fluctuation in the ability to cope with everyday social interactions? As an example, I was posting a valuable watch to a watch repairers the other day. In the post office I was fine, working out with the member of staff what form of postage with insurance would be the best. All went off really smoothly, I think I even made a little joke. Then I went to the local park and had a wander about. It was a hot day and I thought that I would really like an ice cream. There is a tea room in the park that sells ice cream, choc ices etc.. I couldn't make myself go in and interact with the staff in order to purchase an ice cream. Despite knowing that was what the staff were there to do, and that they would be quite happy to sell me whatever I wanted. Then I walked home, ice cream-less, mentally kicking myself for being totally useless.