Actually I have filed a disablity complaint with my state, because I did end up passing out in the parking lot and getting sick in the lanes, and now they have to have a disablity lane in addition to their SOP at all times. I have also found going early in the morning (like before 6) helps. I have also checked out in jewelry, fishing, and auto.
I have also had some positive interactions at walmart, I have had clerks reprimand people for butting in line and some clerks say "she looks like she does not feel well I hope it is ok with you I am going to check her out first."
I am also suprised that you put your items back (you are too nice). If I am sprinting for the bathroom I usually shove my cart into customer service or just leave them as a statement of discontent with the inadaquate clerkage coverage if it happens regularly.
P.S. I have a friend who plays with her tazsar in order to get rid of long lines. It is fairly successful, except if there are alot of single women in the line then we all get ours out and compare. :)