I would get that too. Anxiety on the lead up to going somewhere, it receding after some time in there and then when leaving it would rise again. The same when walking home.
I had some of the worst anxiety at home due to the meds so that will be part of that but I also think it's about getting used to something and then it changing again. So, I would get anxious going to the supermarket, get used to being inside and then get anxious again because of the tills.
I remember by therapist showing me the pattern of anxiety in exposure and it did go up & down like that. I could never find the diagram she had when I was searching online and could only find the typical one shown in post #3 in this thread:
http://www.nomorepanic.co.uk/showthread.php?t=160784
I think that we have multiple exposures in a lot of things so we get the spike when we change to confront something else even though it's element of the same exercise, like a new exposure has been added.