My psychic/medium friend has talked about this.  When you feel this, you are processing energy you body isn't use to and you don't need.  My wife is slightly sensitive and in the presence of unwanted energy, she is sick.  A spirit guide should not do this.

First be sure you are connected to a loving, caring, spirit guide - then test the spirit.  The fact is if the energies are that strong, they are closest to the earth and not the most elevated to work with in spirit communication.  Reach higher through exercises of communion with spirit guides.

I agree that wasn't your guide, you will feel love from them. I have gotten sick to my stomach before when I have visisted certain homes or even part of the highway at times. I think  you are picking up on residual energies where you are at. I went to visit a home one time that we were thinking of buying and literaly felt like I was going to throw up as soon as we left. I started to
feel sick when I was walking around in the back yard and garage. For me it felt like a warning it wasn't the right place, I
listened. Thats what your intuition is all about.
Donna

In the beginning of your relationship with your spirit guide they can come on strong - then as you learn about one another and get it moving right, there is no discomfort.  So any discomfort you feel would be random spirit - an interloper - not your spirit guide.  

Immediately you felt pain or discomfort - and your mind registered it - it would change how the guide works.