it really depends on what is going on in my life but it seems like every 2-3 months for sure but sometimes i can remain in this state for a month or sometimes a could have many short spells in a shorter time frame. Exams are always a trigger for more than the obvious reasons; it was a unspoken tradition for use all to go down to my friends house after are exam to wait for the bus. We would get stoned and munch out and just relax to help with the stress involved with exams. I really find myself missing both the tradition and the therapy it gave.