The purpose of this study is to evaluate how hyperbaric oxygen therapy (HBOT) may affect cognitive functioning, post-traumatic stress disorder (PTSD), depression, anxiety, and overall quality of life in veterans.

1. Does Hyperbaric Oxygen Therapy improve cognitive functioning, psychological well-being, and quality of life among veterans, as measured by pre-and post-treatment scores?
2. To what extent does Hyperbaric Oxygen Therapy improve cognitive functioning, psychological well-being, and qualify of life among veterans, after controlling for demographic characteristics.

Inclusion Criteria:

1. At least 18 years of age.
2. Veteran status
3. Clinically diagnosed with a mTBI, PTSD, Anxiety, or Depression disorder by meeting the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, and by a qualified and trained professional.
4. The subject is willing and able to read, understand, and sign an informed consent. Additionally, the subject has clear consciousness and the ability to express self-feelings independently.
5. Exposed to at least one trauma-focused therapy or evidence-based psychotherapeutic treatment, such as prolonged exposure therapy, EMDR, or CBT, to name a few.
6. Completed cognitive and psychological measurements.
7. Clinical diagnoses cause significant impairment in social or occupational functioning or some other functional capacity.
8. Sexually active female participants of childbearing potential and sexually active male participants with female partners of childbearing potential must agree to use an acceptable method of contraception for the duration of the study and for 30 days following the final HBOT session.
9. Stability on any current psychoactive medications (antidepressants, anti-anxiety medications, antipsychotics, stimulants, and mood stabilizers).

Exclusion Criteria:

1. Untreated pneumothorax
2. History of spontaneous pneumothorax
3. Severe sinus infection
4. Upper respiratory infection
5. Asymptomatic pulmonary lesions on chest x-ray
6. Uncontrollable high fever (greater than 39C)
7. History of chest or ear surgery
8. Congenital spherocytosis
9. Any anemia or blood disorder
10. Any convulsive disorder
11. History of optic neuritis or sudden blindness
12. Middle ear infection
13. Diabetes mellitus (insulin therapy)
14. The subject is pregnant or lactating
15. Nicotine use/substance use/addiction
16. Acute Hypoglycemia
17. Diagnosed Chronic Obstructive Pulmonary Disease (COPD) and Emphysema
18. Presenting with symptoms of cough, congestion, vomiting, diarrhea, or open wounds.
19. Active malignancy
20. Current manic, delusional, or psychotic episodes
21. Serious/current suicidal ideations
22. Severe or unstable physical disorders or major cognitive deficits
23. Inability to attend scheduled clinic visits or comply with study protocols.
24. Treated with HBOT for any reason prior to study enrollment.
25. Non-English speakers
26. History of retinal repair, including laser photocoagulation or retinal detachment surgery.
27. History of middle ear surgery, including tympanoplasty, mastoidectomy, or pressure equalization tube placement.
28. Age greater than 75 years.
29. Use of any of the following medications during the study period: Anti-metabolites (e.g., methotrexate, azathioprine); Chemotherapuetic agents (e.g., cyclophosphamide, cisplatin); Mafenide acetate e.g., Sulfamylon); Disulfiram (e.g, Antabuse); Peripheral vasodilators known to interact with oxygen exposure (e.g., nitroglycerin); and Antibacterial drugs with known HBOT interaction risks.