WINNING --- loosing

[Noen]

From mid July to august 20th I had a ROI of about 28 playing 11$ Speed Sit and Gos at Party. Played around 700 tourneys. Made good money. Then after 20th august, I suddenly started loosing. Get drawn out very often, loosing most coinflips, loosing most hands when solid favorite, rarely win with AK, never get better than third place and so on. I don't think I have changed my game. What was a solid winning game, suddenly became a loosing one. Is this just a variation in luck? Or could Party be rigged; put winning player on loose so that money get distributed to weaker players -- a way to build bigger player base. Some people suggest it is rigged ... What I think is strange, is that the shift from winning to losing is so abrupt and clear. Fluctuations don't seem normal. Anyone else have experienced the same thing? What are your thought upon this matter? I feel like quitting Party after such a bad run. What would you experienced Sit and Go players do in my situation???