What could be causing my fatigue, brain fog, numbness, body aches, and blurred vision?

Differential Diagnosis and Systematic Evaluation

Your symptom constellation of fatigue, brain fog, numbness, body aches, and blurred vision most likely represents orthostatic intolerance (particularly POTS), post-concussion syndrome, or post-viral neuroinflammation (including long COVID), and requires immediate orthostatic vital sign assessment as the highest-yield initial diagnostic step. 1, 2

Immediate Diagnostic Priority: Orthostatic Assessment

Perform an active standing test immediately by measuring blood pressure and heart rate supine, then at 1,3,5, and 10 minutes of standing. 1, 2 This single test can identify:

• Orthostatic hypotension: Drop in systolic BP ≥20 mmHg or diastolic BP ≥10 mmHg within 3 minutes 3
• POTS: Heart rate increase ≥40 bpm (ages 12-19) or ≥30 bpm (ages ≥20) within 10 minutes without significant BP drop 1, 2
• Delayed orthostatic hypotension: BP drop occurring after 3 minutes of standing, which is frequently missed if you only measure for 1-2 minutes 3, 4

Document whether your symptoms (lightheadedness, blurred vision, fatigue, brain fog) worsen during standing and improve with sitting/lying down—this pattern strongly suggests orthostatic intolerance. 2, 4

High-Priority Differential Diagnoses

1. Orthostatic Intolerance/POTS

This is the leading consideration given your specific symptom cluster. 1, 2

Key features supporting this diagnosis:

• Fatigue, brain fog, blurred vision, and generalized weakness are classic manifestations of orthostatic intolerance 3, 2
• Symptoms triggered by standing, heat exposure, meals, exertion, or morning hours 2
• Frequently associated with recent infections, chronic fatigue syndrome, and joint hypermobility 1, 2
• Almost all POTS patients have comorbid conditions 1

2. Post-Concussion Syndrome

Even without recalled head trauma, consider this diagnosis. 3

Symptom overlap is striking:

• Fatigue, brain fog ("feeling foggy"), numbness, blurred vision, and body aches are all documented post-concussion symptoms 3
• The cognitive-fatigue cluster is the most prevalent subtype in concussion patients 3
• Ocular-motor dysfunction causes blurred vision, difficulty with visual focus, eye strain, and frontal headaches 3
• Many concussions go unrecognized—ask specifically about any head impacts, falls, or whiplash injuries, not just "diagnosed concussions" 3

3. Post-Viral Neuroinflammation (Including Long COVID)

Brain fog, fatigue, and body aches are hallmark features. 3, 5

Characteristic pattern:

• Brain fog, fatigue, and breathlessness are the most commonly reported long-term symptoms after COVID-19 3
• Neuroinflammation causes cognitive difficulties, reduced endurance for mental tasks, emotional instability, stress sensitivity, and disproportionately long recovery times after demanding tasks 5, 6
• Symptoms persist beyond 4 weeks after acute illness 3

4. Vertebrobasilar Insufficiency

Less likely but potentially serious. 3

Red flag symptoms:

• Dizziness, vertigo, diplopia, perioral numbness, blurred vision, and ataxia suggest compromised vertebrobasilar perfusion 3
• However, these symptoms can also be caused by cardiac arrhythmias, orthostatic hypotension, and vestibular disorders 3
• Requires vascular imaging if suspected 3

Essential Laboratory Evaluation

Order these tests immediately to identify treatable causes: 1, 2

• Complete blood count: Anemia exacerbates orthostatic symptoms and causes fatigue 1, 2
• Comprehensive metabolic panel: Electrolyte abnormalities, renal dysfunction, and hypoglycemia can mimic this presentation 1, 2
• Thyroid function tests (TSH, free T4): Thyroid dysfunction contributes to fatigue, brain fog, and orthostatic intolerance 1, 2
• Complete iron studies (serum iron, ferritin, transferrin, TIBC, transferrin saturation): Iron deficiency is a recognized contributor to orthostatic intolerance and fatigue 1, 2
• Inflammatory markers (ESR, CRP): Elevated in systemic inflammatory conditions causing neuroinflammation 1

Cardiovascular Assessment

• 12-lead ECG: Essential to evaluate for cardiac conduction abnormalities and establish baseline rhythm 1, 2
• 24-hour Holter monitoring: Consider if palpitations are prominent or symptoms suggest paroxysmal arrhythmia 1, 2
• Echocardiogram: Reserve for cases with prominent cardiac symptoms or suspected structural heart disease 1, 2

Advanced Testing (If Initial Evaluation Inconclusive)

• Tilt-table testing: Only if active standing test is inconclusive but symptoms strongly suggest orthostatic intolerance 1, 2
• Brain MRI: Not routinely indicated unless there are focal neurologic deficits, severe persistent headache, or concern for intracranial pathology 1, 2

Critical Clinical Pitfalls to Avoid

Do not dismiss these symptoms as "just anxiety" or "just dehydration" without objective orthostatic testing—this is the most common diagnostic error. 1, 4 Many patients with orthostatic intolerance are misdiagnosed with anxiety disorders when their symptoms are actually physiological. 2

Do not measure orthostatic vitals for only 1-2 minutes—delayed orthostatic hypotension requires 10 minutes of standing to detect. 3, 1, 4

Do not overlook medication side effects—diuretics, vasodilators, antihypertensives, and sedatives commonly cause these symptoms. 4 Review all current medications.

Do not assume absence of loss of consciousness rules out concussion—LOC occurs in less than 10% of concussions, and brain fog may be the best predictor of slower recovery. 3

Symptom-Specific Considerations

Brain fog represents cognitive dysfunction with impaired concentration, information processing, memory, and mental clarity. 5, 6, 7, 8 It occurs across multiple conditions including orthostatic intolerance, post-concussion syndrome, post-viral syndromes, and neuroinflammation. 5, 6, 7 The underlying mechanisms likely involve astrocyte dysfunction, mitochondrial dysfunction, blood-brain barrier disruption, and microglial activation. 6

Numbness in the context of your other symptoms suggests either peripheral nerve involvement, cervical strain (common with concussion), or sensory symptoms from orthostatic intolerance. 3 Cervical strain causes neck pain, neck stiffness, and persistent headache often with numbness. 3

Blurred vision occurs in both orthostatic intolerance (as "tunnel vision" or "graying out") and post-concussion ocular-motor dysfunction (with difficulty focusing, convergence problems, and photophobia). 3, 2