My very dear Kevin,
Four things you can do when you are being harmed by spirits, for example, when you feel a spirit is pressing down on your chest, etc:

1.  Generate yourself as Yamantaka and then the spirit cannot harm you.
2.  Visualize the spirit as the guru / deity Yamantaka.
3.  Use the experience to meditate on emptiness.
4.  Develop compassion toward the spirit.

How to meditate on emptiness

Seal these three things in emptiness: The harm giver – which is the spirit; you, which is the object to be harmed; and the action of being harmed. See that these three things are not inherently existent, because they are dependent arisings, which means they are merely imputed by mind. Meditate that these three (subject, action, and object) are not truly existent.

One simple way is to think that these three things are not true, meaning that they are empty (what appears from its own side is not true, then you see it as non-existent, empty). Meditate on this and then think these three things are empty because they are dependent arisings. Meditate on the meaning of the Prasangika view, the extremely, subtle dependent arising, merely labeled by the mind, which makes you see reality – that is empty.

The first method, meditating on emptiness, eliminates eternalism. The second method, dependent arising, eliminates nihilism. This is the middle way view on emptiness, which is a very powerful method, and is the Prasangika view.

You can meditate on these verses from the Three Principal Aspects of the Path, by Lama Tsongkhapa:

Appearances are infallible dependent origination;
Voidness is free of assertions.
As long as these two understandings are seen as separate,
One has not yet realized the intent of the Buddha.

When these two realizations are simultaneous and concurrent,
From a mere sight of infallible dependent origination
Comes certain knowledge that completely destroys all modes of mental grasping.
At that time the analysis of the profound view is complete.

Appearances clear away the extreme of existence;
Voidness clears away the extreme of non-existence.
When you understand the arising of cause and effect from the viewpoint of voidness,
You are not captivated by either extreme view.

How to develop compassion towards the spirit

Think that the spirit is totally overwhelmed by delusion and ignorance, with a totally hallucinated mind, as well as under the power of karma and disturbing thoughts. Think that the spirit is in samsara, completely overwhelmed by suffering, and generate compassion by reflecting in this way.

Each time the spirit harms you, the spirit creates negative karma, which causes him or her to be reborn in the hell realms, or again as a spirit, hell being, or animal, and to again harm you and others, create negative karma, be continuously born in the lower realms, and experience unimaginable suffering again and again.

Another method to develop compassion is to think if I were already enlightened, liberated from samsara, not suffering, not under the power of karma and delusion, then the spirit could not harm me, therefore the spirit would not create negative karma by harming me, because from my side there would be no cause to receive harm from the spirit. So, the spirit wouldn’t create heavy negative karma by harming me.

You meditate on these verses from the Three Principal Aspects of the Path:

Swept by the current of the four powerful rivers,
Tied by strong bonds of karma, so hard to undo,
Caught in the iron net of self-grasping,
Completely enveloped by the darkness of ignorance,

Born and reborn in boundless samsara,
Ceaselessly tormented by the three miseries –
All beings, your mothers, are in this condition.
Think of them and generate bodhi-mind.

Also, you can think that in the past you have caused the spirit harm, which caused him or her to engage in negative karma and harm you in this life. Therefore, you deserve to receive harm from the spirit now. This is your karma because you have harmed the spirit before. So, this is the result of your past karma. The conclusion is to not harm others, practice samaya vows, and protect your karma – cause and effect.

So, use this to develop compassion. Think: “I must do something to liberate the spirit, so therefore I must practice Dharma.” The conclusion is, in order to really benefit other sentient beings, to not harm other sentient beings, and to benefit sentient beings, you must actualize the path to enlightenment. Therefore, you must first achieve enlightenment and the quickest way to do that is by actualizing the Three Principles of the Path, particularly tantra, so that you can quickly lead all beings in the path to liberation and enlightenment.