I agree with Ultranomad.
The symptoms of too-high g-forces are loss of color vision (greyout), tunnel vision, blackout and eventually loss of consciousness (g-loc). These symptoms all occur because the brain, and in particular your eyes (which are most sensitive to this) do not get enough oxygen.
Oxygen is delivered to your brain by your blood. It's your blood pressure, generated by the heart, which pumps the blood upwards to your brain. Under normal circumstances, your heart is able to pump blood about one meter upwards (that's the reason that IV bags are hung relatively high). The vertical distance from your heart to your brain is about 25 centimeters. So a normally proportioned, normally fit adult should not suffer from any g effects until reaching, approximately, 4G.
There's a lot more science involved and there are several aerobatics books that cover this in a lot more detail, and with a lot more accuracy. But at 60 degrees bank angle you should only be pulling 2G and that's nowhere near enough to cause g effects. Even if you've done negative g's just before (which you have not). (Although if you go to 75 degrees angle of bank - just 15 degrees more - you need to pull 4G already and that might trigger g effects. But in a typical training spamcan, your cruise, full power and stall speeds are so that you will barely be able to sustain a 4G/75 degree steep turn for long enough for g effects to manifest itself.)
As Ultranomad says, it's probably nausea. You can get desensitized to this easily just by flying a lot, particularly steep turns and other unusual attitudes/aerobatics. There are also several exercises you can do on the ground. Here's a scientific paper on this subject:
http://medind.nic.in/iab/t07/s1/iabt07s1p37.pdf
And here's a site of a doctor that sells DVDs. Haven't seen those myself though (I stumbled on it searching for the link above), but it might be worth a look:
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