Shares at PSX fail to sustain early gains, dip by 500 points / Shares at PSX rebound as investor confidence returns / Shares at PSX rebound after bearish previous session / Shares at PSX climb 800 points after IMF announcement / Shares at PSX climb 800 points on positive economic outlook / Shares at PSX reverse gains after upward start as Pakistan-India tensions loom / Shares at PSX reverse gains after upward start / Shares at PSX climb 900 points on strong corporate results from heavyweights / One of UK's largest companies sees PS2bn wiped off shares through north American market weakness / Shares at PSX reach all-time high before reversing gains