Hi Mushy
When levels are pretty good at 5ish, and levels raise so rapidly, I really believe that there must have been 1) Airbubbles 2) a 'suckback' in the tubing if you took the pump off whilst showering. probably or 3) a kink near the lueur connection possibly the tube being tight there.
I too have experienced exactly the same as you, but my occasions like this have all been down to the above 3 reasons.
1) I found my levels always go up 5 hours after a cartridge change, but I now do a lot of banging and priming 4 hours after a cartridge change
2) My levels had risen badly one morning,as overnight somehow (don't know how) the whole connector and lueur had come undone
3) The lueur connector had the tubing accidentally pulled really tight sideways (and no-my pump didn't warn me of an occlusion)-my levels just went high
4) I completely disconnect to have showers and baths, and Accuchek do not tell you that during this time insulin can go back up the tubing-some other websites call it 'suckback'. I also find this happens, and I can see the insulin drawn back about an inch up the tubing, and this for my pump equates to about 3 units to pump through before I reconnect it to me. Otherwise I will go without insulin for up to 8 hours whilst it gradually feeds that air out.
Please Mushy, don't go changing anything basals or bolus immediately, do your extra bolus as you have done, and please don't panic or think about quitting the pump.
I personally doubt very much if it was anything to do with your body at all. I firmly believe it would be one of the reasons above, and these problems can be resolved.....honest.