Hypothyroidism or myxoedema is where the thyroid gland produces too little thyroid hormone (thyroxine) which has pronounced effects on the rest of the body.
The thyroid gland controls the body's metabolic rate and so, in hypothyroidism, the metabolic rate is slowed down, resulting in the following symptoms:
In most cases it is caused by the thyroid cells beginning to fail and thus less thyroxine is produced. This can occur without obvious cause or can be after the body developing an immune reaction against itself or after an operation to remove part of the thyroid gland. It can also be caused by some medication e.g. lithium, amiodarone.
If you have some of the symptoms above you should consult your doctor. He/she will take a blood test to determine your thyroxine levels and will usually then prescribe thyroxine tablets for you to take daily. If you have a history of heart problems the doctor will start you on a low dose at first as thyroxine increases the work rate of all the cells in your body. Your system will have been used to functioning at a lower rate for some time and so, as with starting any exercise regime, it is sensible to build up to a higher metabolic rate in stages.
You should have regular blood tests whilst on thyroxine to check your blood levels, as recommended by your doctor.