I did an IHM course this weekend and really struggled when others were practising the face on me. We used cushions rolled up at the back of the neck and then rested the 'clients' head back on this and also on our body. Most people seemed fine but I found it very painful on my neck and would worry that my client would also feel this. I also struggle when holding my head back in yoga back bends so I assume it is just me but others might experience discomfort if they have ever had a neck injury.
What do you use??
Hi breeze,
Yes I too was taught to rest their head on my body and I found it could be difficult for some people to relax.
I now do IHM with the person sitting on the treatment couch and I have it set to the lowest height that it will go to (it is an electric one so will go quite low). I pop a knee pillow underneath their knees and also one under their ankles, if I am going straight onto Reflexology afterwards, so they are all set up and do not need to be disturbed again. I have the back vertical and as I reach the face I slip a small pillow under their neck for support.
Feedback for this is good, most people drift off at this point, it certainly works for me! 
If it is seated I would lie the persons head against me wih a tolled up rowel behiind their neck. If I am going from a massage into IHM I would leave them on the pillow I use during a body massage.
I find a small pillow is comfortable for my clients. Are you perhaps bending your head back, Breeze? I always make sure my client's head is upright.