I think Angel's advice is good, though in my case, I'm not having a lot of luck in figuring out why. As someone who used to be incredibly analytical and very "cerebral", for want of a better term, I am often horrified at my lack of mastery of some of those basic but critical higher order cognitive processes, such as planning, problem solving, time management, task prioritisation, etc. I become easily overwhelmed by too much information, too many choices or options, or too many steps involved in a process that would lead to a simple straightforward course of action.
I think that PTSD in itself causes a degree of overload in the brain that can act to limit or partially shut down some of those processes. No, that's not based on science, but merely on personal observation and an attempt at interpretation of what goes on for me.
I also think that other key symptoms such as sleep disturbance, hypervigilance and general high levels of stress and anxiety have the same limiting effect.
In the end, trying to understand, trying to limit stress, trying to put in place as many little cognitive aids and supports as possible, and, importantly, trying not to beat ourselves up about it, are the best weapons.
Maddog