Hi there, I am Dr. Deepak, I work in Emergency Department, where I see many patients with injury to their head. As you mentioned you had injured your head while doing sit-ups, after which you had watery discharge mixed with small amount of blood. Now you are feeling alright, except for the headache. I feel you had sustained minor injury to your head, I can say that as 1. You didn t had any dizzy feeling. 2. You didn t had vomiting even though you had nausea. 3. You didn t loose consciousness. 4. You are not feeling any numbness or weakness of any one side of your body 5. You are not having any bluish discoloration around your eyes and behind the ear 6. You are not having any trouble with walking. And the most important thing is you are pretty much okay right now. If you face any of the above mentioned problem within 24-48 hrs, then you can show to the Doctor, who can examine you. Your headache might be because of injury or may be because of some other reason, can t tell for sure. For the time being you can apply some ice pack over the injury area, take some pain killer for the pain and take rest for sometime. If the headache persist for more than 48 hrs then you should a doctors for further treatment. Thank you Hope your concern was dealt with and hope you have a speedy recovery.