Have I got more stupid?

I'm finding it harder to read papers. I've had a skim through some of the older blog posts. They sounded smarter and I used more big words. And swore a lot less too.

Is it the effect of isolation, less stress, less drugs or some brain deficit? I've slowed down a lot over the past few months. I could whip through a paper quickly but now it's taking me ages to read a reasonably short paper on the IAPT scheme (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5W-4WS2HYG-1&_user=10&_coverDate=11/30/2009&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1433582937&_rerunOrigin=scholar.google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=4d3538d879039c6b22d4e007572e7565)

I was taught that mathematics is like a knife. Keep using it and it stays sharp. Leave it alone and it becomes blunt. I hope that's true. If I lose my intellectual capabilities then I've really got nothing left to offer.