What should the headache while having accutane feel like?

The very concerning headache actually caused by Isotretinoin is called Pseudo Tumor Cerebri.  It is actually quite rare, but if you have the symptoms, you need to stop the medication immediately and call your dermatologist.  The symptoms are an unrelenting headache that is not relieved by anti-inflammatory medications such as ibuprofen and the headache will continue as long as medication is continued.  There is often a visual change with blurred vision.  The headache usually resolves within 1-2 days after stopping the medication.  Certainly, if your headache does not stop after several days off the medication, you should contact your primary physician.