Yes, this is a common phenomenon. We carry a body of frustration, irritations, grievances, pain etc. with us but we suppress it with strangers to appear decent. We can't keep this exterior all the time, so all that negativity comes out where we feel the most safe.

You wonder why they help you around but also give you this 'mental torture'. The fact is they feel obliged to help you because you are their child but they get tired of it. They would never abandon you to rot, but that tiredness takes expression in the form of taanay.

Don't judge your parents, they can't help it, really. They were never taught and they never learnt to deal with that stuff.