In regards to diffusing them, are they all innocuous, or is it possible for essential oils to make you nauseous/headache-y/dizzy?

I have two primary coworkers in my office suite. One of them has been using a Scentsy for several weeks. The other has, in the last week, brought her essential oil diffuser and has been using that. I did just fine with the Scentsy, but for the past week I have regularly felt nauseous, dizzy, and had horrible headaches while at work. When I go home, I’m usually fine after a short period.

At first I was thinking it was the competing scents, in early college I worked at Bath and Body Works for a number of years, but now I have a hard time going in there because it’s scent overload, but I never get the nauseous and dizzy feeling, just a bit of a headache. For that reason, I’m starting to think it may just be the essential oils that I’m reacting to, but I don’t know. I’m trying to do research, and I’ve seen that many suggest only diffusing them for 15-20 minutes for newbies and 1-2 hours for experienced users. My coworker diffuses it from the time she gets into the office at 7:50 to presumably after I leave at 4:00.

If it helps, the scents that I’ve been told she uses are Lavender and Peppermint (diffused together), and Patchouli (I assume diffused on its own).

Is it possible that the oils could be affecting me? Or are they really innocuous and I need to be looking for a different source to my sudden sickness at work?