If you use Win7 this will most likely solve it for you. Right click on your swtor.exe go into compatibility, tick the box that says Run in compatibility mode, select Win exp Service pack 3. Start up the game and all should be normal once again. Not 100% sure why this worked, think it had something to do with the engine not liking win7. Hope this works for you Click here for better optimization and other solutions
99% of the people here had to do this the first day the game went live just to get it to run.. so i doubt this will help.
the problem lies in the the fact that the game optimizations they made for 1.3 effect specific CPUS it seems. People with I5 systems are reporting an increase in FPS while everyone else, especially those with mid and low range pcs (which this patch was supposed to be for) are reporting huge loss in FPS just like before the optimizations in 1.2.