Veins never burst for no reason. there always is a reason. you just dont see it.
Have a full blood count with platelets, pt aptt
INR and clotting factors study. also do a doppler duplex ultrasound of lower extremety to rule out any vasulopathy. and to brain bursting of vessels occur but that is most of the time arteries due to hypertensions, atherosclerosises, aneurysms, traumas etc.
so stop worrying and have your self checked. i am sure it would be nothing