Many of us suffer the occasional headache. But when does a headache become something more serious? The majority of aches are harmless. These include sinus headaches, tension headaches and migraines. Some may be enough to put you in bed all day, but can be alleviated with painkillers and will go away in due time. Other headaches may not be so easily curable and could be the sign of something serious like a stroke or tumor. Here are few times when you should be concerned.