I now wear a mirror when riding

[malkin]

That 'look at the image' thing worked for me. I used to get sick looking at the mirror too.

I gave up on my mirror though because I kept knocking it off my glasses and I got better at turning to look behind me anyway.

[Catrin]

I have straight bars there are bar-end mirrors work made for them I use the Mirrycle Mountain mirror and I wouldn't cycle without it. I've no desire for other types of mirrors - you will find fans here of all of the different types of mirror for the bike. Experiment and find what works best for you. My mirror is quite steady/stable and also inexpensive - I don't think any of the mirrors are really all that expensive which makes them easy to replace should something happen.

[BleeckerSt_Girl]

I love my helmet mirror. Once it broke, and I felt terrible- like one would feel if driving a car with no mirrors.
Mirrors are wonderful things. And yes, you should always use a quick head glance too whenever possible- just like you do when you're car driving.

I use a "Third Eye" helmet mirror.

And yes, helmet and eyeglass mirrors take getting used to. After a few days or weeks (depending on how much you ride) your brain and your eyes adapt to the strange newness and then typically you just love it.
One tip- when you are just starting with a mirror attached to your head somewhere, don't look at it all the time- just glance at it sometimes (like maybe when you hear a truck approaching far behind you) and adjust its position. You'll start to get used to it more naturally that way than if you keep obsessively looking at it.