The headache and upset stomach are likely related to Food Poisoning. But, if you find the headache worsens when you stand up quickly it may be from low oxygen levels in your bloodstream. If you feel light sensitivity it means you could be getting a Migraine which is known to cause upset stomach. If you vomit than you should go see a GP within the next 24 hours, if you vomit 2 or more times and/or get severe diarrhea you need to see a GP tonight.
If you notice any dis-coordination, nausea or rapid heartbeat you may be suffering from a more serious condition and need to go to the E.D. immediately. Upset stomach and headache is a symptom is a varying degree of illness ranging from not serious at all to potentially life threatening. Having said that though until more symptoms start to arise it's best to assume your body will fix the problem.
In all likelihood, you are fine. Relax.
Source: My Wife is a Doctor and I had to help her study a lot.