It's a survival mechanism.
Extreme heat, e.g. fire, and extreme cold, e.g. ice, can be fatal to humans. So nature has equipped us to feel sensations, ranging from discomfort to pain depending on the intensity of the heat or cold, in order to warn us of the potential threat.
People who have impaired sensitivity in their fingers or toes (maybe due to a medical problem like Diabetes) have to be very careful because they are at greater risk of burns as they cannot feel when things become hot.
After my head injury I have cold sensations internally
Measuring the temperature with adequate instruments.
When they feel hot they think it's hot n feel cold then they feel cold
These are the five feelings 1. Hot 2. Cold 3. Pressure 4. Touch 5. Pain
Sounds like peripheral neuropathy
No. Nor are they necessarily indicators of ambient temperature change.
Because you are sick
If you have a heated item and put it in a normal temperature water, it feels cold because the hot water may feel so hot that it is cold. It's the opposite for the cold item.
It's bad if you can't feel cold because your body is supposed to be hot or cold. If you can't feel cold, see a doctor.
you probably have a cold or a flu, I feel like this when I am ill.
Spirits don't exist (if you mean, like, ghosts), so there can't be any "good spirits" or "bad spirits" giving off warm or cold sensations and feelings...
When you get hot, if you drink cold water it will make you feel good.