Congrats!

One week is fairly recent in the grand scheme of things. While you are probably through the worst of the withdrawal it might be that your neurology is still coming right. So... Hang in there, it might well be that you are still going through some kind of 'rebound' effect neurologically.

In addition, I guess it would take a little longer for the psychological addiction to remit. Part of the psychological addiction can be such beliefs as 'I'm not as smart / as quick in my thinking off caffine' etc etc. Those kinds of beliefs can make it a self fulfilling prophecy.

Now... I could be talking out of my *** here... But I'll have a go. My impression of the drugs that make you think better (caffine, nicotine, cocaine, amphetamine) is that they kinda work like this:

(This is a schematic model to be sure, but I think it works fairly well to illustrate the point. It is strictly speaking false but I think it could be made to be true by complicating it somewhat. I'll go with this model for simplicity)

Lets represent your baseline cognitive ability as '50'.
When you take some caffine / nicotine / cocaine / amphetamine then lets represent your temporarily improved cognitive ability as '60'.
When the drug starts to come out of your system then your cognitive ability decreases towards the baseline of 50...
But then you have the rebound effect such that your cognitive ability keeps on decreasing past the baseline of 50 down to a new low of (let us say) 40.
That is about when you start saying to yourself 'jeepers I better have another cup of coffee) which perks it back up to 60.

Only... After a time... That next cup of coffee doesn't get it back up to 60. Instead... It takes you to 55. And the comedown can be more severe (35, let us say). This is called TOLERANCE. Eventually that cup of coffee takes you to 50 (which was precisely where you were BEFORE you ever started taking the drug). Only... You don't notice because the NEW DIFFERENCE is the same as the OLD DIFFERENCE (so on caffine you are 50 and off caffine you are 30 whereas the very first time you took it on caffine you were 60 and off caffine you are 40 so it is a difference of 20 either way).

So... rebound of 20 and I bet you do feel like your cognitive abilities are not so good :-(

The good news is that over time your cognitive abilities will return to your old baseline and you will be caffine free.

A similar thing happens with people taking sleeping medication and the like... People experience the rebound effects when they stop taking them and say 'OMG I really NEED that drug!!!' Or they think that they have 'come right' on the drug whereas they have no idea whether they would have 'come right' off the drug, and they have no idea how much better they would be doing overall if they stopped the drug (after rebound) now.

Anyhoo... Hang in there, sounds like you are doing FANTASIC