Mentally Exhausted...

How does it feel to have your hopes raised and dashed at the very next moment??? That is what has been happening to me for the past...countless number of months...everytime I think I am moving closer to forming my dissertation topic...my hopes will be dashed after consultation with my Prof...haiz...i cant take this anymore...this dissertation is really draining all my energy...i cant concentrate on anything else...I'm neglecting my other 2 modules...I dont even feel like doing anything...whats happening to me? Why am I letting this bog me down to this extent...the desire to do well...its starting to take a toll on me...I cant take it much longer....help!