You're not tripping, you just have to dodge with your sword looking down so you're invulreable to side, and upward attacks, but the ai tries to switch do an attack from above, switch stances to counter.
For the low fps, check Drasnus's solution, I'll copy and paste it here for ease of use:
The game is running at half-speed (30-40fps consistently, feels sluggish and slow):
Try opening the options.ini file in notepad and changing 'AlternateSyncMethod' to 1.
You can also try running the exe in compatibility mode.
Also try installing Visual C++ 2012 x86 and x64.
And finally, turn on visable fps so you can see if it's the fatigue or just your computer. Also, it's buggy because it's more of a demo or initial version of the game, if you check the update logs you'll see Drasnus is constantly working on the new version. Hope this helps :)