I have experienced headache after orgasm, but sometimes i don't experience it, is it bad?

Post orgasm headaches are common. Orgasm frequently increases the body's blood pressure level or cerebrospinal fluid pressure. If you experience headaches consistently after orgasm, you may want to have a full check up to determine if there is anything physiologically unusual and to rule out other serious causes such as arterial dissection and subarachnoid hemorrhage.

The presence of sudden intense headaches at time of sexual climax has been called "thunderclap headaches" and is a variety of migraine. Preventative medications for these headaches are often highly successful. Discuss some approaches with your doctor.