It's awful when you have weird dreams about them, same as when you lose a person you love and you dream they're there and when you wake up you realise they're gone. After my cat died I had dreams where all my cats were still alive but in some sort of danger and I was having to collect them all up in a single cat carrier to make them safe. You're actually relieved when you wake up from that type of dream. At first you can't help feeling guilty about putting your animal to sleep but you gradually accept that you did what was right. I think it takes a lot longer than a week to feel anywhere near normal.