You're crying because at the moment this is what you need to do. We usually don't cry without good reason so be kind and patient with yourself. Therapy can be very painful - if emotions need releasing crying is a natural response. It can be very draining but unless you feel this is happening excessively i would try and relax and accept it as part of the therapy process - it won't remain that way forever most likely and if it does, well you're in therapy! you have a safe place to work through it!