My doctor says that I need a pacemaker. What is it. What will it do? Will I be hospitalized, etc?

This is a long question. Are you asking about these people? We may not know anything about outcomes and experience of the surgeons if we don't live in the area.

Take him to the hospital for a check up

Yes, because as an in-patient you are under the hospital doctor's care, and that doctor should know more of your immediate condition than the GP does.

Normally a report would later be sent or carried by you to the GP about what has happened, and it would be unusual for the GP to object. You could try asking the hospital doctor to consult with the GP if you feel there are things the hospital doctor has not noticed.

If it is just that you are not sleeping, that is not unusual in a hospital, I cannot do myself. Ask for a sleeping pill of appropriate type.

It is all done for your welfare.

You are a specialised case with a pacemaker. I'd make a wild guess that it needs reprogramming but that's far from certain. You must get back to your doctor for advice.
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From what I know a CT scan is considered safe for those with a pacemaker, but a MRI scan is not.

Just make sure the doctor and radiographer know you have one, it will be routine for them. Also ask if an ultrasound is a possible option for you. These are routinely used to look at kidneys.