Periodontal disease is an infection in the gums from dental plaque bacteria.  Periodontal disease used to be called pyorrhoea, but this term is no longer used.  There are 2 kinds of periodontal disease:

a. Gingivitis which is red swollen bleeding gums.

b. Periodontitis which occurs when the infection causing gingivitis starts to damage the seal between the guns and the teeth and creeps down under the gums to form pockets of infection that slowly erode away the supporting bone and gum tissues over a period of time.  This results in receding gums, loosening and moving teeth, and in the later stages, gum abscesses and painful teeth, often accompanied with bad tastes and bad odours in the mouth.  Once the teeth reach this stage they usually have to be extracted as they are untreatable.
However the earlier you get the problem under control, the less damage has occurred, and the best chance of keeping your teeth for the rest of your life is set up.

Any signs of bleeding, redness, tenderness, or swelling of your gums that does not disappear within a couple of days, should be checked out by a dental professional.  Because the gums are not usually painful most people tend not to worry about the problem until it is too late and their teeth are moving, getting loose, their gums and teeth are becoming painful and sensitive and they cannot eat and speak properly.

By that stage it is too late to do anything so the sooner you get it checked out and dealt with the better, even if your gums are not painful.  Hygienists and dentists are usually very good at identifying the problem and treating it, but some are better than others.  If the treatment you are being given isn’t solving the problem, you can always get a second opinion from a periodontist. (i.e. a dentist who specialises in treating periodontal diseases).

Yes, it can be very successfully treated providing it is caught early enough.  So the sooner you get it seen to the better chances of successful treatment.
If you do have periodontal disease, even in its very early stages, you may need to accept that you have to go to the dentist/hygienist/periodontist more frequently than other people who do not have this condition.  It also means that you have to be much more careful about cleaning your teeth than other people who seem to be able to tolerate some plaque in their mouths.  Treatment involves teamwork between you keeping your mouth as plaque free as possible, and your dental professional getting to the parts that you cannot reach.  In the same way as diseases like rheumatoid arthritis, diabetes, cannot be “cured”,  it can be managed so that the tissues remain stable and the disease process is halted, which means that you do not end up losing your teeth in the future.

Periodontal diseases is treated by you and a member of the dental team getting your mouth into a sparkling clean state.  Even if you manage to clean your teeth perfectly you can only clean your teeth above the gum margins.  Below the gum margins you need professional help so the treatment involves cleaning up the debris and dental plaque that has accumulated underneath your gums.  This sounds horrific, but actually it is not!  It is a bit like the dental equivalent of cleaning under your fingernails except that you cannot do that in your mouth.  Sometimes it can be painful if the condition has progressed or your teeth are very sensitive in which case you may need to have the treatment done over 4 to 6 sessions, cleaning different parts of your mouth at each session with injections being used to numb your gums.
I do not actually work that way because I was trained to clear out as much of the debris as possible throughout your mouth in a single appointment.  This means that I work very quickly and get the problem out of the way swiftly and efficiently without you having to come back for repeated long dental appointments .  A session of treatment usually lasts about three quarters of an hour and depending on the extent of the problem I may need 2 or 3 appointments.  In extreme cases it may be necessary to do surgery and sometimes to graft bone infill materials around the teeth if too much bone loss has occurred.  Once again, the earlier you get treatment the less complex and the more successful it will be, and surgery will probably not be necessary.  After completing the treatment phase you will probably need to go back to your dental team as regularly as 3 monthly for repeated deep cleaning until the gums heal up fully.

Most people know that they need to clean their teeth.  However what most people do not know is that you need to clean your teeth and gums.  Making sure that your toothbrush is always partially on your gums and giving them a good cleaning, to ensure that no plaque is left behind is the best way of making sure that the bacteria in dental plaque do not start to infect your gums.  But what most people do not realise is that a toothbrush cannot clean your mouth effectively.  The filaments of a toothbrush cannot get in between your teeth, so you need additional cleaning aids to get into difficult areas like this.  Your local chemist probably stocks a whole range of interdental brushes specially designed to get in between your teeth and into those little nooks and crannies that plaque lodges and starts to grow and damage your gums.  Sometimes in some places you cannot get the brushes in you may need to use dental floss as well, or even a combination of different sizes of brushes and dental floss to make sure that there is absolutely no plaque left in your mouth.  It is always a good idea to get a member of your dental team to identify areas that you are missing out and give you specific ways of making sure that you are getting into all of the little difficult areas that a normal toothbrush does not reach.  So get professional help to make sure that you are doing it properly!