Terro is correct, Amethyst is a fine stone to use for protection against nightmares, bad dreams and drunkenness, and it does have some healing properties too, however if a psychic attack is part of the problem, which it sounds like it could be, then you would do much better to use a clear quartz crystal instead. Clear quartz is not only an excellent protection stone for day and night, it also has strong healing properties. Unlike Amethyst it strengthens the psychic abilities to help guard you against any psychic attack, either intentional or unintentional, and will also help you raise your inner power so giving you the chance to better protect yourself.
Cleanse it and programme it for it's intended use by using the methods given here:
Moon's crystal cleansing and programming instructions.Posts 3 and 4 give clear instructions on how to cleanse and programme crystals and stones.
Then place it under your pillow as you sleep. When you wake up make sure you put it in your pocket or somewhere so you carry it with you all day, when you sleep again return it to your pillow. Having it with you around the clock will help protect you, if you feel it needs recharging place it in a sunny spot for a few hours, or if it needs cleansing again repeat the cleansing process but be sure to reprogramme it again afterwards.
I looked for any of the white light protection spells that Terro said were easily available on Google, but couldn't find one that I would recommend you to use.
However my mum had one that she says is simple and effective.
{{She also says that if you haven't already been checked out by a doctor for your mysterious cuts then Terro's advice about seeing one and being checked medically is very good and should be followed ASAP, just to be certain that you do not have a medical problem which is causing this.}}
Protection SpellSit comfortably on the floor with a clear quartz crystal in your cupped hands. (If you chose a clear quartz crystal for protection against psychic attack while you sleep like I mentioned above, then you could use the same one for this aswell.) Light a candle and gaze into the flame. Breathe softly and evenly and when you feel calm and relaxed imagine yourself taking the energy of the flame into you. Absorb it through your skin and feel it glowing warm and protective just below the surface. Surround yourself with the energy from the candle, feel it as though you had stepped into the candle flame and were surrounded by the cleansing, protective heat of the candle. Now say these words:
I craft my protection from flame,
I guard my essence well.
Those who mean me harm,
find no way through my spell.
My inner power guides my way,
my inner strength revealed.
The energy of fire,
adds it's power to my shield.
As you say the words visualise a shining golden glow surrounding you, covering your body, and standing about 12 inches from the surface of your skin. See that no harm can enter, any negativity just burns up on contact with the flames, leaving you calm and unhurt inside your protective shield.
Breath gently in through your nose and out through your mouth. As you breathe out channel some of the energy you have raised into the crystal with each breath. Do this for a few minutes, feeling the energy settling into the crystal. It will quickly absorb the energy and you carry the crystal with you either wearing it as jewelery or placing it in a pocket. If you ever feel your shield slipping or you think you might need an extra boost all you have to do is touch the crystal and it will give you what you need.
One last point to mention is that you should never put crystals or stones into plastic bags. Energy and Magic needs to flow and breathe, and a plastic bag stifles that. If you want to protect it and allow it to breathe then wrap it in a piece of silk cloth, or if silk is something you cannot get hold of then a plain cotton hanky or a piece of a cotton tea towel will do the job just as well, and you can buy them cheaply from almost anywhere.

I really hope this post has helped. If you need to contact me for any reason then please, please do. I am usually around and do check in regularly even though I do not always post.
This is actually something I am trying to fix as I have been very neglectful of this forum lately and hadn't really thought of it until I had it pointed out to me by a friend.