Let me just say, I've been in the spot that you are currently in and I get how maddening it can actually be. You get all prepped up to work out, finish all your tasks on time, attend to the chore, are probably only a workout away from living your dream life. But, your body has other plans and just decides to be as uncooperative as is bodily possible. Well, that is what happened to me every time I tried to do a few crunches, sit-ups, or any exercise for that matter.  

So, I saw a doctor, and thank God I did because not only was the annoying phenomena now explained, but I can give free advice to you as well.  

Improper diet

This may be the core reason that you are experiencing headaches during your workout routine. Your body isn't getting enough nutrients to use as fuel in the very first place. So, your blood sugar levels may be low, hence the unexplained headache. In order to treat this cause, try and add more proteins and vitamins to your diet. Take a healthy snack or smoothie before you begin working out.  

Exertional Headaches 

The second reason as to why you are feeling the way that you are maybe because of this. Exertional headaches are caused when blood vessels in your body are unnecessarily dilated. This happens because when you exercise, your body muscles need more blood circulation. The best way to treat this is to keep yourself hydrated, slowly build up in your exercise routine and take pain killers. 

Are you worried due to the headache you get post workout? Are you afraid something went wrong during your strenuous workout? These are common thoughts striking your mind, especially to those who are beginners and/or who are unaware of the reason.  

The headache caused due to workout is called as exertional headache. Exertional headache is caused when the body undergoes some strenuous physical activity such as workout, coughing etc.  

The pain either occurs on both sides of the head or just one side. In majority of the cases, the pain is fixed all by itself within a few minutes or so. A few people may suffer from it for days too.  

There are two types of exertional headaches- primary and secondary exertional headache

Treatment: It is normal if your head hurts post workout provided there are  no other symptoms. If you do have other symptoms, you should consult the doctor to overrule any underlying problem.  

Prevention: Drink water before and during workout to avoid dehydration.

It is not unusual to have a headache after you workout. Apart from headache, you may feel restless too which is totally normal.  

But why do we get headaches after the workout is the question? The answer to which is quite simple, due to extensive and strenuous workouts, the blood vessels narrow down demanding more supply of blood hence, the headache.  These headaches due to the exertion are called exertional headaches. 

Exertional headaches are of two types;

1. Primary exertional headaches: Experts say, it could be due to narrowing of blood vessels which occur due to workout. 
2. Secondary exertional headaches:  This is also due to workouts but it accompanied with an underlying health issue.

Since, both primary and secondary exertional headaches occur due to workouts, how can we differentiate between them? Well, the secondary headaches are accompanied with other symptoms which makes us easier to figure out which category of headache are we undergoing through. Symptoms include: 

• Vomiting
• Neck stiffness
• Congestion
• Vision problems. 

Treatment:

• Stay hydrated
• Warm up before performing 
• Workout in a relatively cooler environment or place. 

                  

Headache post workouts are normal and can happen due to a couple of reasons. Personally, I get them often and they go away within 5-10 minutes.  

1. Dehydration 

A person gets dehydrated due to excessive loss of fluid from the body as compared to the intake of fluid. Chances of you sweating during workout is high which holds accountability for dehydration. 

2. Exertional headache 

Headaches which occur due to any form of strenuous physical activity is called exertional headaches. Due to the pressure on the body, the blood vessels narrow causing less blood supply to the brain resulting in headache. 

3. Heat 

People working out in sunlight often get headaches. Choose a cool place to workout. If you can't, then make sure you wear sunglasses and a hat. 

4. Hypoglycemia

Low blood sugar levels also known as hypoglycemia can also cause headache post exercising. It is caused due to hunger where in the glucose is burnt for body's energy. Hence, a person should eat enough before working out. 

       

If you get a headache every time that you work out or engage in complex physical activity, you are most likely to experience an exertional headache. Don't worry about it though, it isn't something that you need to be worried about or that requires medical attention or care.
As for why it happens, it is because your blood vessels dilate since it needs more blood to be circulated to the rest of the body such as your head, scalp, and your neck. In such a scenario, you should drink water or any hydrating drink to energize yourself and if you can, chew a piece of gum or suck on a toffee, it should keep your blood sugar levels intact.