Dear Consider,
Valid points have been made but I must add......

Insomnia I believe in this instance to be caused by the subconscious becoming aware of an unresolved issue. Normally when we have a problem, the brain breaks it down into small pieces , disects it and resolves. Due to brain trauma you are temporarily not able to do this.
Your accident has changed your life so rapidly that your body cannot keep up.

So at night when you should be calm enough to sleep your brain is screaming at you that something is wrong but you in your conscious mind do not know what and so every time you close your eyes where your subconscious should take over and work in the form of relax and dreams, it too is full of anxiety and unresolved issues. There you get insomnia.

Anxiety is a physical reaction caused by the body becoming overloaded and not breaking down problems faster than the problems are compacting. This also causes depression.

Panick attacks are part of fight or flight. Your body believes because it has entered a temporary situation that is new, that it must be wrong. ie hit head, new symptoms that are not resolving quickly and so the body believes it is better off dead.

So you get palpitations, shortness of breath, sweating, shaking and the brain goes into overdrive and really believes you are dying.

The best way to deal with a panick attack is to let it happen. Remember it cannot kill you. Some people however have been known to to go onto develop a heart problems based on not dealing well with constant panick attacks.

In your case you will probably benefit well from councilling. This speaking therapy will aid your brain, teaching it to learn how to break down your problems again and prevent them from compacting, causing anxiety, panick attacks and insomnia.

Good luck.