I just did this this morning! My friend is getting married Sunday (yikes!!!) and I am doing ALOT of the decorating (double yikes!!!) Anyway, I was in the garage putting some finishing touches on some of the decorations; and I started coughing, like I was gonna puke. I decided then that it was too hot for me and I went into the house.
So, two things I have found that set me off:
gross things (blood--weird since I am a doula)
heat (I live in the high desert! We will be spending the summer traveling up the west coast, where it is COOLER!!!
I really don't think it is psychological, since i really don't have a queasy stonach around blood normally. I have always been the "nurse" in my family. Whenever anybody got injured, I was the calm one, and treated them without worrying about blood or nastiness. Also, I am a doula, and love the birthing process. I don't get queasy around blood EVER!!
And, I have lived in the desert all my life, and have never dry heaved because I was running around in 65-70 degree weather!
PS-- I don't have "morning sickness," either, just periodic queasiness-- not every day, and not at the same time every day.