Essential Thrombocythemia (ET): This condition is characterized by chronic thrombocytosis, which the patient has had for 7 years. The presence of giant platelet forms and the absence of other clear causes of thrombocytosis (like inflammation or iron deficiency) support this diagnosis. ET can lead to symptoms such as headaches, dizziness, and fatigue due to microvascular disturbances and possible thrombotic events.

Polycythemia Vera (PV): Although the patient's RBC count is currently normal, PV can sometimes present with isolated thrombocytosis, and the anemia that has resolved could have been a phase in the disease's progression. PV can cause similar symptoms to ET, including headaches, dizziness, and fatigue.
Chronic Myeloproliferative Neoplasm (MPN): This category includes conditions like ET and PV but also considers other myeloproliferative disorders. The patient's long-standing thrombocytosis and family history of autoimmune diseases and hypertension might suggest a predisposition to MPNs.
Fibromyalgia: Given the patient's family history of fibromyalgia and symptoms like fatigue, brain fog, and possibly the gastrointestinal symptoms, fibromyalgia could be contributing to the patient's clinical picture, especially if the primary hematologic condition does not fully explain all symptoms.

Thrombotic Thrombocytopenic Purpura (TTP): Although the patient has thrombocytosis rather than thrombocytopenia, atypical presentations can occur. The symptoms of headaches, dizziness, and fatigue could be indicative of TTP, which is a medical emergency.
Paroxysmal Nocturnal Hemoglobinuria (PNH): This rare condition can present with thrombocytosis, anemia (which the patient had), and symptoms like fatigue and shortness of breath. PNH is a life-threatening condition that requires prompt diagnosis and treatment.
Systemic Lupus Erythematosus (SLE): Given the family history of autoimmune diseases, SLE should be considered, as it can cause a wide range of symptoms including hematologic abnormalities, although thrombocytosis is less common.

Primary Myelofibrosis (PMF): This is another myeloproliferative neoplasm that could present with thrombocytosis, although it more commonly presents with splenomegaly and progressive bone marrow fibrosis leading to cytopenias.
Hereditary Thrombocythemia: This could be considered given the long-standing nature of the thrombocytosis and the absence of other clear causes, although specific genetic mutations would need to be identified to support this diagnosis.