I was playing witcher 3 on my laptop a few days ago and it was running nice and smoothly. I got it to work on high graphics with hairworks turned off at 50 fps with my gtx 780m. Today I started witcher 3 again, but it was extremely laggy. The game was running at about 15 fps, so the first thing i tried was turning everything to low. Still only 20 fps. I don't know what happened over the last few days but something isn't right. I checked my gpu drivers but they are all the most recent updates. I tried restarting my laptop many times and checked if witcher 3 is maybe using the intel integrated gpu and not the nvidia one, but nothing helped so far.
Any ideas about what else I might try?

This may sound stupid but have you checked to make sure that your laptop is still plugged in or that the power settings haven't changed? If there was an interruption in power your laptop may have switched to a "balanced" mode rather than a "performance" mode to conserve power, which automatically scales back on some of the more power-hungry hardware (such as the GPU) and reduces performance. I've had it happen to me before.

Haven't played for a few days,maybe Galaxy or Witcher is updating while your playing?

Checked it both. The battery settings are still on performance and my laptop is plugged in. Neither gog nor witcher was updating so that's not the reason. The only thing I remember that could have changed something is a windows 7 update I installed today, but I don't know if that might have affected the performance.

Could it be something with the shader cache ? Can't imagine why but with computers and going wrong anything goes.

Even Nividia's hotfix drivers haven't worked and the game is still unplayable even on low settings. I also tried clearing the shader cache but no improvement. I'm really frustrated as I enjoyed playing the game quite a lot and it's suddenly no longer working. Even uninstalling and redownloading it twice hasn't worked. Do you guys have any other ideas or suggestions I might try?

Do you have an onboard graphic card besides your "normal" graphic card? If yes, perhaps the game uses the onboard chip. If so try to disable the onboard graphic card.

Hmmm. I've had quircky things happen from time to time to my game where I've had to piddle around with game restarts and such.

Maybe try uninstalling that windows 7 update you mentioned. I know there's one update that Microsoft snuck in on me a couple of times that's related to their upcoming windows 10 upgrade.(shows a little white windows logo in the taskbar) I don't recall it affecting my games but I got rid of it because of its invasive nature.

Another game issue I've noticed personally is that sometimes the game will sneak itself into borderless window mode on me for some reason. I think I've figured it out too. I use a controller for the game but usually I can tell that the game will start with mouse cursor automatically. As the game starts I'll click the mouse on the opening window a couple of times then proceed to use the intended controller. I've noticed that when I do this and check my video options, the game is full screen as I've set it. If I allow it to load the game without clicking on the mouse during load,(I think somehow its starting in borderless window mode) when I go check settings it will be in borderless window mode.

Not sure if any of this helps. Maybe try downloading and installing an older driver, perhaps even several back like the first NVidia driver to come out for the game's release if you can find it.

This could be interesting for you: https://forums.geforce.com/default/topic/528621/can-39-t-disable-integrated-intel-hd-graphics/

Have you tried to disable the integrated gpu in the bios?

Just to make sure: have you installed any mods before the game started behaving strangely?

Thanks a lot for all the help. I finally got it to work again 30fps on high graphics :D I'm not exactly sure what cause the drop in performance as it was suddenly working again this morning. I guess it was mixture of all. I'm running the nvidia hotfix driver 353.49 right now, unistalled all the windows updates and played around with the graphics card settings. It was one of those three things that probably fixed it for me.

Haha, that's nice. Have fun with your game again!