Don't believe that at all.
Very common occurrence on CT,Prius and Auris (UK).
None have been due to head gasket failure. This engine doesn't suffer from head gasket problems and I've never read of any either.
Does the engine suffer from coolant loss?
Are you having to keep topping it up?
Is there any oil in the water and water in the oil?
Which cylinders are misfiring ?
Mine had this problem last winter. I cleaned out the EGR valve and pipe and used a fuel injector cleaner. The car hasn't suffered with it since. It was also a really scary bad shuddering too.
Sorry for the questions but I would investigate it more as you don't want to be paying for things that aren't required.
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Did you do the work yourself, or have it done? I'm shitting myself right now with this loud shuttering. Two mechanics on the phone have told me it's the head gasket from what I describe. I'm not very mechanical, so would probably have it done, if in fact it's what you say. I haven't had the car looked at yet. Not sure how I would request this service. Just ask them to clean the EGR valve and pipe? Did you put fuel injector into your gas tank? Which brand? Thanks so much...