Benn there myself mate, totally wrecked. What I think you need to do, without knowing to much about you or what you eat and stuff you do in your life, is have a look at that.
You say you are physically worn out, is that with any damage to yourself muscle and joint wise. Are you physically able to do things?
Look at the food you eat and the water you drink. Cut out sugars and processed foods, and fast foods to. These, whilst great in moderation... who doesn't like the odd cake or piece of choccy, are energy sappers and feed only the bad bacteria and stuff in your body. If you are down, they are not what you need. Fresh fruit and veg of the best quality you can afford, and if you live in a flouridated area
www.wmaf.org.uk/userfiles/Map%20Fluoridated%20Regions%20of%20England%202002.pdf start getting bottled water to drink and make you tea with. A water filter is good even if you don't, the brita variety, as it takes the chlorie out. If you can afford it a water distiller is the best option. Also cut out the low fat margerines and other crud. You need full on butter, milk and animal fats. Milk and butter is best off been organic then you can be sure it doesnt have antibiotics and bovine growth hormone in it... plus it is less likely to be contaminated with puss and crap, as the non organic processes rely more on pasturisation to make their product safe... which it doesnt really with all that crud in it. These fats are essential building blocks for your body and enable your body to metabolise vitamins and minerals properly.
Then you need to have a look at some supplements. I personally would start with Vitamin D3... why, because that's where I started. If you are pretty down and feeling cruddy or are a big person I would start on 10,000iu a day during the winter and only 5000iu a day in the summer. You can pick up 360 tablets for £14.74 on amazon at the moment, and it supports your health and immune system marvelously. This one supplement was a total life saver for me, and the more I found out about the more I was amazed by it. I would also add in a bio-available multi vitamin (synthetics cannot be processed by your body and only give you expensive piss.. they are also the crap they try to slander supplements with in their lying studies) and some pro-biotics. Your gut has a MASSIVE impact on your all round health and well being, and if you don't have enough good bacteria in their to counteract the bad one the bad ones run rampant and allow your gut to absorb things into your body that should not be there... effecting everything from mild mood swing to actually causing mental disorders, ie the depression and forgetfulness you are experiencing.
There are many other things you could add in, MSM for example for your joints and pains, though from some stuff I have been looking at recently, but have yet to experiment on, Organic Sulphur seems a lot better, but I will have to get back to you on that one.
Essential Oils may also be of benefit to lift your mood. Lavender or Peppermint diffuse in your room could lift your mood, there are many that could help you.
Note... None of this is medical advice, just things I have found out that have worked for me and turned me from a depressed, forgetful, unable to move wreck sleeping 20hrs a day, hardly able to move and on more drugs than a Mexican Cartel to more than normal, still have a few physical problems, but apart from that I am off medications totally and using diet, supplements and alternative health "Cures" to sort myself out these days. This is not also a total list of all the things I use. For example STOP USING TABLE SALT. Get yourself some Celtic Sea salt... proper salt, not the chemical crap they give you.... and stop using sugar and artificial sweetners