The first tests you need to have done, to determine a
thyroid issue, would be Free T3, Free T4, TSH and
thyroid antibody tests.
Are you being treated for the low B12? This can also cause strange symptoms. Have you been tested for diabetes? Diabetes can cause the excessive thirst you described, as well as light headedness, your feelings of detachment, mood swings and many others.
Most of these issues are very easily treated, once diagnosed.