I have two thoughts on this -
First since you came back to the safe, it's opened with keys and the door was OPEN? THis was your memory, you went to it, took out the cash for the Christmas thing.....took out the envelope, took out the $100, had that envelope in your hand, got distracted, and thought.......(WHAT)......I'll hide it here, for the moment instead of putting it back in the safe......and then had a brain poot.......or SOmeone is coming I don't want them to know so I'll put it HERE......(had a brain poot) had the envelope in your hand and walked (WHERE)........Personally at this point? FOr that sake? I'd go see a psycho therapist and ask to be hypnotized. You're under a lot of PTSD stress, and you WILL remember under hypnosis where you put it.....because you WANT to remember......but right now you're too stressed to remember -----you're brain remembers but your stress won't let you and a pro could unlock that memory. Okay - so that's the good thought.
The bad thought is that you did NOT leave the door open, and NOT to be greedy ------a thief OTHER than a family member and I'm sorry to say K and M came right to mind.....Have gotten a copy of your keys....and unbekonwn to you KNOW about the safe, the money......etc.....and took ONLY what they needed.....so that they wouldn't TIP off the cops.....slipped in, got what they needed, and slipped out. That way----being clever (and no that's not their strong suit) but.....a ring is traceable and basically worthless at a pawn shop because ......well it's traceable) and cash is not. I'd be watching to see if the fantastic family there has a BRIGHT windfall from a lotto ticket or a GREAT christmas - new car......bragging rights on a shiny bike for every kid. Yeah....Can't prove a thing.....but have you thought about asking your neighbors if by chance they saw anyone around your house while you were sleeping? And maybe the dogs didn't bark because WHATEVER???? I don't know. Obviously not my first pick.......of thoughts.
Best of luck to you hon......