Not having enough enough oxygen in the body and indeed the brain can have terrible effects in the life of a person.It could affect your daily life, friendship/relationships etc. Let's take time to find out what could possibly wrong with us or around us especially when it lingers for some time. The following are the effects of not having enough oxygen:
1. Damage to specific brain regions deprived of oxygen. Various brain regions tend to coordinate different functions, so some functions might be severely crippled, while others remain intact. For instance, the injury survivor might be able to understand language but unable to speak.

2. Changes in mood or personality.

3. Difficulty with memory, including the ability to recall facts, names of objects or people, recognize faces, learn new information, or recall autobiographical facts.

4. Changes in motor skills. A number of brain regions help coordinate movement, so if these areas are damaged, you may struggle to walk, write, or engage in other functions.

5. Chronic pain. When the brain is damaged, it may incorrectly process pain signals, causing you to feel pain even when there is not an injury.

6. The inability to feel pain, or to correctly respond to pain signals. For instance, pain in your arm might feel like pain in your leg.

7. Difficulties with impulse control. Many brain injury survivors develop addictions, aggressive behavior, or sexually inappropriate compulsions.

8. Symptoms of mental illnesses such as depression or anxiety.

9. Dementia-like symptoms, including confusion, memory difficulties, and signs of rapid brain aging.

Somethings that can be done to increase oxygen in the body:

1. Make sure your apartment/office is well aerated.

2. Go out for a walk.

3. Do more exercises.

4. Eat less fat. Etc.

Don't always think that you are under any demonic attack or something because of strange feelings in your head. Check your environment and make a change.

You can google too find out more symptoms and what could be done.

source: https://www.spinalcord.com/blog/what-happens-after-a-lack-of-oxygen-to-the-brain