Sophia, I speak as a retinal detachment patient. The only way to tell what's going on and what treatment is needed is for you to get a dilated exam, preferably by an ophthalmologist although where I am you have to go to an optometrist (what we'd colloquially call an optician) for exam and to get a referral to an ophthalmologist if needed.
Dr. Hagan may well be right in thinking this could be nothing to worry about. But if you really do think it's serious (and even if you don't - just for your own peace of mind), I'd advise you to get an exam now. Optometrists can often very easily make emergency appointments to see you if you mention these symptoms - they are standard "red flags" that they know to look for and they will make time to see you if you mention them. Mine will often see me the same day, and I have seen them multiple times since my surgery when anything new crops up. Whoever is examining you will tell you what treatment may be needed and/or make onward referrals to those more specialised in the field if necessary. The advice to get an exam is standard advice for the symptoms you describe (flashes and floaters), particularly if they appear or change suddenly.
Nobody can afford to play around with this eye stuff. Trying to self-diagnose or get diagnoses or treatment plans from people on online forums is taking up time which may be important if your problem really does turn out to be serious. A retinal tear can quickly lead to a retinal detachment which can be blinding and requires major surgery to fix. If you have a retinal tear you can get it lasered to try and prevent it progressing to a detachment, but time is of the essence, and you need to be getting all this looked at now. No matter how detailed you are in your descriptions of symptoms, nobody online can ever make a diagnosis or tell you what treatment is needed.
I'd suggest not discussing this here again at all unless / until you've had that appointment and either been given the all-clear or else been told in detail what is causing these symptoms and what, if anything, further needs to be done in the way of treatment.
Feel free to keep us all up to date on what they do eventually say at the appointment!