Finally did this yesterday, very early, and it was actually not as bad as I feared.
I tried it earlier in the week but had to stop because of stomach cramps after about 11 mins, but didn't worry too much about that, just walked steadily home and reminded myself it was all helpful prep for the next time.
Second time lucky - I trusted Laura and I kept thinking of Oldfloss and Irish John and your fabulous reminders to go sloooooowwwwwwwww Thanks guys, you got me round!