Instant headaches are fusels in my experience. You most likely underpitched and stressed the yeast. If you used a stir plate for your starter you needed 3 liters. If you didn't use a stir plate and made just a simple "sit there" starter then you needed 8 liters.
Also, if you're not controlling your fermentation temps you could have gotten into the high 70's with room temps in the high 60's.
If it smells like solvent and burns your throat and sinuses and gives you an instant headache it is fusels and you are pretty much screwed. Depending how bad they are they may age out so that you can drink it, but I'm guessing that since it's giving you a headache instantly you're not going to want to be drinking too much of it.