Sri Chinmoy 1/2 marathon - Centennial Park

I should be happy with a trophy for 1st O50 and shaving 28 seconds or so off the M50 course record - but I'm not totally.I felt I went off at a good sensible pace but at 8km the wheels just fell off big time.I started to lose contact with those around me then started being passed constantly - counting down each painful km.I'm really not running at all well at present and suffering from real tiredness/injuries whilst hardly doing any mileage.