I completely sympathise and empathise with this - I do similar things all too often these days
I NEVER used to make mistakes like that, but I'm afraid my memory and organisational skills are pants these days. I've turned up for appointments days early, days late. Missed appointments entirely.... I now put reminders on my calendar, on my electronic diary and on my phone. It does work (when I remember to do it!).
I went into the DaVinci exhibition in London yesterday. Got to the station in plenty of time. Let the two Met Line trains go past & got onto the Pic Line train. Sitting playing a silly game on my phone, realised that I better not miss my stop and looked up at the tube map..... to realise that I was supposed to be getting off at Baker Street, which is on the MET LINE! ARGH!!!! Had to stay on the Pic train and use a different route which involved a crazy number of steps and walking (NOT good), plus because I was then running late I had to walk faster than I have done in yonks (REEEEEEEEEALLY not good). Stupid, stupid, stupid!
On the plus side, going to the gym is clearly paying off!
Glad the hospital could fit you in next week