Latency Fluctuation

Hello.
Lately I've been having huge latency fluctuations in-game. I get somewhere between 300- 700 ms. It jumps fairly quickly in that range. Strangely however, a ping test via Cmd prompt, or using Resource Monitor while logged in-game, I see latency as 180-200ms consistently which is my normal latency (since I live in India). Anybody can shine some light on why there is a huge difference in latencies shown in-game vs other methods? Just to be clear, I feel the lag inside game as well. The fluctuation occur in MoP and WotLK realms. No Cata client so I can't check that.

Thanks!