Better safe then sorry

Maybe tape it while you do it, and when you can't remember look back at your tape. Or indeed get some therapy :-)

I have that same problem, though I've never gone back after actually getting on the train. And I've never actually forgotten to lock my door.

You call this unusual I call this normal, for me at least

Sounds like you need to get into some sort of confirming routine - take a picture on you phone or something _after_ you have turned the key so that you can reassure yourself without having to go all the way back.

If you have anxiety probblems like this a freqently, that impact your life this bad, maybe you should seek help? I really do not intend to sound mean. But this is not the first time? It's not a shamefull thing to seek help if needed.

Your not alone doing this I know

You're under a lot of stress. It's time to either plan a vacation or get more sleep and stop drinking during the week. If that doesn't fix the issue, I echo the other commenters and say visit a nice counselor and get some help. There is something very freeing about unloading your issues onto a stranger who can prescribe you medication. I see you live in the UK, if you still have socialized medicine, this shouldn't cost you anything after the referral from your GP. Other than that, maybe your family needs to pick up some of the slack for you, you may be trying to do too much.

All joking aside. It's actually a disorder. You should talk to your doctor before it gets worse.

You more than likely have Obsessive Compulsive Disorder. Go to a doctor to get a professional opinion though. I do the same thing with locking up my house at night, its a right pain in the arse especially when I am really tired and just can't leave the door alone ¬_¬