Smartphone suddenly extremely slow

[Big_Chair]

Hey guys,
I have a weird problem with my Xperia Z:
Since friday it's MUCH slower in any form of reaction.

The only thing that I remeber to be different on that day was that I looked for something on the Internet (using Chrome), was therefore on some pages and then there was a site which was not displayed properly and in the help of Chrome it said to just delete the data of the application, which I did and it worked. At the point everything was ok.
But at some point later in the evening when I used the phone again, I noticed that everything suddenly started to react slowly.

I've already looked in some forums about this but there are mostly just great advices as "try restarting it", which I already did of course.
I also deleted all unnecessary things with CleanMaster and scanned it with avast but with no results.

Does anyone have an idea what this might be?

 

[Big_Chair]

Oh, sorry maybe I worded it wrong.
Not the browser alone is slow, but the whole smartphone, everything that I do, even typing.
I just mentioned the browser because that's the only unusual thing that I did on that day