Why Do I Feel Dizzy And Fainted After Not Taking Clexane Injections?

Hi i have recently ruptured my achilles tendon, and had surgery 6 weeks ago.
I hve made 3 flights during this time and have been prescribed Clexane in jections, I stopped taking it only prior and just after a flight. i am now feeling dizzy and have fainted twice, could this be a clot or teh Clexane?