Two weeks continuous is alright, assuming there was no static image on the screen shown over that time.
Fluorescent lights reach a maximum brightness at a certain temperature. If they get hotter, they run dimmer, such as a CFL operated continuously in an sealed light fixture. As most LCD monitors use florescent lights, the high operating temperature at the time was likely why it appeared dimmer than usual. It should be back to normal brightness now after leaving it to cool.
2 weeks continuous is 336 hours. That's the equivalent to using the monitor for 6 hours / day for 2 months, so nothing all that excessive.
The only time I'd be concerned with is if a static image was shown over that time, which can cause a shadow of this static image to appear. I originally thought that only CRT and plasma displays were affected, but I've seen this happen while in a server room where the LCD monitor for the console showed a strong shadow of the Windows logon screen, likely due to the screensaver and monitor off features disabled on the server.