Markets remained volatile during today's trading session, ahead of the expiry of June series derivative contracts tomorrow. Erasing the day gains, Sensex slipped by over 800 points from its day high on Wednesday, to close at 34,868.98 which is 561.45 points or 1.58 per cent lower than its previous close, while Nifty fell by 165.70 points or 1.58 per cent to settle at 10,305.30.