I have felt the same way-stressed/anxious after having a busy day. It doesn't hit until I am relaxing. At the same time if I am stressed over something like running late to a meeting or trying to do too many things at one time, I will also have an attack. Sleep deprivation is definitely a contributing factor.I try to prioritize between what absolutley must be done (work, chores,tec.) and what can wait until later. Sometimes it works.I think the worse thing with the panic attacks and the anxiety is it is so unpredictable.
