When doing push ups I get a headache in my upper neck/ lower back of my head

I have been training to get in shape to become a navy seal, that said ive been doing swimming, push ups, sit ups, pull ups, and running for a few months.  Recently (last wednesday nov 10) while during my PST, i swam 500 yards then 10 minutes later was doing push ups and when i got to about 30 almost instantly i got a severe headache located just in the back of my head right where the stem goes into the skull.  this then threw off the rest of my work out but i continued because it was a test.  None of the other excersises worsened it but it was there for the rest of the day.  I thought it was because i wasnt breathing enough (doing as many as i could in an alloted time) during each rep, however last night (the 12th) I went to do some push ups (having not worked out since wednesday to allow for whatever i did to heal) it happened agian and i stopped immediately.  I then did situps which again didnt make it worse and then ran. This time when doing pushups i was doing them slowly taking full breaths in going up and out going down and it still happened.  Now im getting worried.... any ideas?

[Dr San Miguel]

Hi. Exercise headaches occur during or after sustained, strenuous running, rowing, tennis, swimming and weightlifting exercises. Most exercise headaches are harmless, and can be prevented with medications, hydration and warm-up exercises. However, headaches related to brain and circulatory problems may require immediate medical attention. It might be best to see your physician for further evaluation and management. Hope this helps.

[gymdandee]

Some people get headaches during exercise. These headaches are completely physiological. Please remember to do warm up exercises. Also maintain your fluid intake throughout the work out.
A mild over the counter pain killer before exercise will also help.
It could also be a nerve. Are you taking any supplements? if you are try eliminating one at a time and see if it helps also see a Chiropractor. could be any number of things

[BrySchmidt]

No, no supplements at all.  I drink water throughout the day, though might not be eating all that great (not enough vitamins).  but ive been doing these workouts for months now and this happened all of a sudden.  

[Dr San Miguel]

Hi. Exercise headaches occur during or after sustained, strenuous running, rowing, tennis, swimming and weightlifting exercises. Most exercise headaches are harmless, and can be prevented with medications, hydration and warm-up exercises. However, headaches related to brain and circulatory problems may require immediate medical attention. It might be best to see your physician for further evaluation and management. Hope this helps.

[kevin3587]

Hi I ve been working out regularly for last 1.5 year... day before yesterday I was doin shoulder exercises end of the season I was getting little headache...today when I went to do exercise, in warm up I did pull ups and got sudden headache I tried to do lat pull down but because of the headache and discomfort I had to stop the exercise.....