You have been very unlucky to have a TIA that has laid you that low. I am so sorry to hear of this affliction. There have been others on this forum who have had several weeks of fatigue etc from a TIA.
Hopefully things will ease for you soon. In the meantime you should rest up and give your brain a chance to combat fatigue. When you are fully rested then you might find it better if you do part time, either say two days a week or say mornings only. Your GP has no doubt given a sick note and that is a good guide. If your employer has an OT then talk to them as well.
Being over stressed can do a lot of damage. I swear by relaxation techniques and I go to "classes" to show me how to relax. A TIA can be a warning shot that your body is over stretched. Consider your fitness, diet and sleep patterns.