Hi, I'd like to help you with your question.
Before I can help, I need to ask a few questions.
Do you have any trauma in your background? A loss of any type?
Have you ever been diagnosed with anything by a psychiatrist or mental health professional?
Do you use drugs or alcohol?
Have you been abused in any way, either in childhood or as an adult?
Wow, it sounds like you have been through a lot.
It does not sound like Post traumatic stress disorder. What it may be is a stress reaction that triggered an illness, brought on by what you are going through.
You have tried to rule out anything physical, which would be my first step in your case. What did the doctor in Essendon tell you that you have?
Although a nervous breakdown is not an official diagnosis in mental health, I do understand what he means. It is a stress reaction just as your GP said. A chemical imbalance is something different and could mean a variety of disorders. I am not sure which one he means.
Acute Stress is one possibility. An anxiety disorder may be another. The heart palpations and panic attacks are signs of an anxiety disorder. Some of your other symptoms fit as well.
I have heard of sick building syndrome. It can cause many of the symptoms you describe. I did find a good resource on it which may help you:
What you may have is a combination of a physical and emotional reaction to the stress you were under. It makes more sense to consider two diagnosis since you do not seem to fit only one. A combination of medication (such as an anti anxiety) and therapy would help your emotional symptoms. If you were able to deal with the emotional issues, your doctor could address the symptoms that are left as medical.
Environmental problems can cause stress enough to create a stress reaction. I am not so sure that they can cause a chemical imbalance, however. Some environmental conditions can cause illnesses, such as cancer, but I do not think they just cause a chemical imbalance.
Chemical imbalances are usually related to such illnesses as schizophrenia, severe depression, thyroid issues, and other endocrine system issues. You can see an endocrinologist to check for chemical imbalances in the system to see if that may be an issue for you. They can do extensive testing through blood work and urine tests to check your levels and let you know if you do have an imbalance.
You may also want to consider moving out of the home you are in. If you feel it is causing these many symptoms and you are sick, then it is not worth it to stay.