I could be wrong,
but tickling, in its basic form is hardwired in our brain as an exercise in recognizing danger..kind of like a cats stomach- although it might even feel good to them - their brain says its an extremely vulnerable position, and essentially nothing "foreign" should be touching this area.
so... this begins the fight or flight response and boom, the adrenocorticotropic hormone stimulates the release of adrenaline and dopamine( stimuli and pain killer in case of injury) the cat scratches you and runs away.
if you'll notice, ticklish areas are the same as vulnerable areas.
Feet(if we were still primitive{and yes even though we have smart phones and what have you, our mind still answers to its primitive forefather} an injury to your foot could be lethal)
thighs and armpits are right over arteries
stomach, and ribs are of course protecting your vital organs
Since were humans and we spent most of our history evolving our minds, some of us enjoy the "controlled" release of these chemicals...we seek that which scares us a little.. but not too much, and thus fetishes are formed.
To answer your question, and I'm sorry about the long post, but i had to set a basis of information for my theory- if you don't receive the proper aftercare, or absolute reassurance, your mind begins to turn on what you once found so endearing, and sees it for what it COULD only be- an exercise in recognizing danger, and not a consensual act between adults.
A tried and true method i use for my lee's, and this is only if i have to rush out the door, the very last thing i do (after i've massaged her, helper her come down, talked to her a bit and got her something to drink) is drop to my knee and rest my head against her stomach- and she knows- even though i may be in control at times, it is her choice and decision, she is the one with all the power.
there is this pic floating around the inter-webs of a girl with a collar and a leash and the caption reads something along the lines of "the power lies within the collar"
But what do i know. I'm just an electrician.
Hope I helped, sorry if I didn't
🙂