Propanolol is a beta blocker. It works by stopping the cells in your body absorbing adrenalin and so even if you produce loads of adrenalin because you are scared or anxious, it wont produce as much of a physical effect on your body, so less heart racing, breathlessness and scatterbrain-ness
There are a lot of different beta blockers that work in different ways, so if one has side effects that dont sit well with you, you can try another one.
They tend to be fast acting, but if you have been taking them for a while, you body adjusts, so ypu have to wean back off them or you can get a rebound
Citalopram is a SSRI. These are drugs that slow the speed at which your body breaks down serotonin and so as a result it increases serotonin levels in your body. Serotonin is the key hormone that stabilizes our mood, feelings of well-being, and happiness. This hormone impacts your entire body. It enables brain cells and other nervous system cells to communicate with each other. Serotonin also helps with sleeping, eating, and digestion.
It takes 4-6 weeks to get to a level in your body that will impact you and again has to be weaned off. Doctors usually start with a testing dose to see if you get bad side effect and then go up to a active dosage about 2 weeks later. There can be some significant side effects, but some people have none at all. Its very much a trial and error process. There are many other SSRI s that work slightly differently so you might have to try a few before you find the one that suits you
If I were you I would go to the GP and ask if they think you should see a psychiatrist to discuss your symptoms or if they GP is willing to prescribe for you. If GP is willing to prescribe then ask about their thoughts on Beta blockers versus SSRIs versus combination of the two.
Most clinical studies show that they most effective way of tackling anxiety and depression is a combination of drugs AND medication
Good luck OP, dont be fobbed off. Write a list of questions and take notes on what the GP says, you can ask them to repeat stuff, say you dont understand and ask them to try explaining it again. You can also say “so what I am hearing you say is xyz...is that correct”