Yikes! Emacs line mode went crazy and its persisent...please help!

[butzwonker]

Is that even possible? After years of using Emacs, today I might have pressed 
some presumably incorrect keyboard combination and now Emacs in AucTex has 
started to go crazy. I used to have visual-line-mode and line numbering on. Now 
suddenly it wraps to some column (98) instead of the window with and if I press 
ctrl-e it jumps to the next line. When I go back with ctrl-b it doesn't jump to 
the last word on the previous line but to the last position in the visible 
frame! Then, when there is e.g. "the" on the current line and I type " dude", 
"the" jumps to the previous line and "dude" moves to the beginning of the line.

Also, the line numbering now shows one line per paragraph instead of 
consecutive line numbers for each soft-wrapped line. 

What's puzzling me is that I did not make any changes to default.el or .emacs 
and nevertheless the change is persistent across Emacs launches and even 
logging in and out again. It happened from one moment to the other, so it must 
have been caused by an unusual keypress.

Does anybody have an idea what I inadvertently changed? Please help, this is 
driving me nuts and I can't work that way.

GNU Emacs 24.5.1 (x86_64-pc-linux-gnu, GTK+ Version 3.18.9)
 of 2017-09-20 on lcy01-07, modified by Debian