Still, calm, tranquilize your mind. Talk to this entity as though it were a person in your ordinary world.
Such things can happen by accident. Generally we have 'shields' (really just agreements between peoples ... now being ignored wholesale by data miners ... that are usually not breached, but sometimes two people can have such complimentary thoughts that one can slip into the consciousness of another.
One also becomes aware of the non-existence of real barriers between minds when practicing meditation. This is why training in good will and ethical conduct is so important a prerequisite for successful meditating. Become aware of your thoughts and trim them up properly.
Example: you may find yourself worked up about politics and focus on some leader with anger at his positions. Think about what the results of that would be if you were face-to-face with this leader. Your interactions with 'phantom' beings in meditation must be as carefully conducted as are your relations in the so-called 'real' world.
Invasion of another's mind is really only contact with another's mind. This being is not 'inside' your mind, but is only able to influence it as in a face-to-face conversation. But when the invadee is unaware (and almost everyone is unaware), a malicious invader can pretend to be the other's mind and this will be perceived as 'my thoughts' by the victim. If you feel the force is malicious, practice metta: "May you be well and happy!" With Feeling! And, oh yes, I nearly forgot: ulimately, no thoughts are 'your thoughts'; if you can see that, your problem is solved. Short of that you need to strengthen your identity with the Dhamma such that outside forces are easily recognized by you.
If you are being attacked because you have done something harmful to this entity, apologize. If you don't know what you may have done, ask. The answer should make your symptoms look like a simile for the problem and its results. Figure out what you should have done and let this entity know you are attempting to change.
This is likely also to be physical. The idea of an invading entity and physical disability is not mutually exclusive. But throwing off heat is frequently a symptom of purging of poisons (which could be the result of some bad deed done to this entity) and is a good thing when the throwing off is complete. If you cannot get any response from this 'entity (but be careful, response may not be as you expect; the communication may not be verbal, it may be pictorial, it may be a startling intuition) assume it is internal to yourself and look for either a habit you should break or a habit you are breaking that has withdrawal symptoms. Age too can cause symptoms such as you describe.
Take the Refuges. Find a Bhikkhu near you and ask to be given the refuges. This is the first step in becoming a Buddhist and, doubt it if you will, is powerful protective magic power. Then get involved in Sutta Study. The mind recognizes the superior power of the clear thinking that is contained in the suttas and by attention to that rises above the scope of malicious entities. Guaranteed!
Here is a link to the Sutta Index of multiple sets of sutta translations. Start from the first, or jump in anywhere: most suttas were given to people who would never see the Buddha a second time and so were constructed such as to lead to the goal no matter how brief the instruction.
Of course you can also stick with the consensus reality that such things do not exist and end up in an asylum because you are crazy.