I've been using my bike just about the same really. But it's worse when it's hot, because I have been contantly hot for the past five months at least (even if it' cold outside) [it's not swine flu or anything. Been having the windows open and the fan on no matter what the weather. Even tried tying a battery operated one to my bike!
lol Didn't work (probably would have if I used masking tape though). Got an appointment with an endocrinoligist on the 9th, so hopefully get some answers (cos there's other symptoms too that I've had for years), though the appointment is outpatients and it should have been a 24 hour one.