Short term memory loss.... you just need to wait long enough for it to shift into long term memory, then you'll be right

Should occur to you in a few days, it's happened to me too with online passwords.
Tip: Use a childhood phone number, postcode or somesuch that is no longer related to you, but still memorised.
For online combo's use a significant word, drop a letter midway and use an old postcode Eg. kan3000aroo