For a medium to communicate with spirit people there has to be an overlap of energies. When the energies merge and overlap there is a sharing of information, not just of the mind and thought, but of physical senses too.
For example, if a spirit person wishes to let the medium know that they passed over with a heart attack, they will send the signal to the medium's nervous system and adrenal glands (with help from the spirit guides) the medium's body then manufactures the sense of the heart attack. The medium will feel the heart beat change, thump more heavily in their chest, become quickened or slowed. They will also feel the pins and needles that are often present during an attack and they will feel the pain in the chest and the dizziness associated with it. Although those symptoms sound distressing the medium will not feel them to a degree that is incapacitating and will sense a milder form of the attack. However, when working with guides and spirit communicators there is alot of learning to do on both sides, so it's important for the medium to take control and know their own limits. If for example, the sensation of a heart attack was becoming strong and overwhelming the medium must tell the guides to stop transmitting the information. They have no desire to harm the medium but neither do they know how sensitive the medium is to their frequencies, communication is an ongoing experiment as everyone has different levels of toleration.
The medium must practise regularly for communication with spirit in order to interpret the signals that their body receives. The medium must study the symptoms of illness too so that sensations are correctly interpreted along with a basic understanding of anatomy.
When a spirit wishes to communicate sadness the medium will feel the sadness, the energy will remain strong and it feels like a strong downward pull within the heart chakra, a sinking feeling and the energy will feel flat. When a spirit communicates happiness and a bubbly personality the solar plexus is used and it feels like a tickle, the medium can't help but smile, the energy is lifted and becomes vibrant and is usually clearly transmitted. When a spirit wishes to convey a stroke the medium will feel a pain in the head, loss of sensation in the affected limbs and a dizzy feeling. If the medium is unfortunate enough to feel the energy of a suicide victim the appropriate parts of the medium's body will be affected, a hanging will be felt as a tightening around the throat, sometimes the object used for suicide or murder is felt within or around the body too.
Sharp pain felt by the spirit will be felt as sharp pain by the medium but will be weaker so as not to cause distress to the nervous system. Someone who was blind will affect the medium by blurring or obscuring the vision, the medium is often left in no doubt about symptoms and conditions felt by the spirit during their life.
This type of mediumship is called physical. Many mediums who work clairvoyantly or clairsentiently don't acknowledge that this part of their mediumship belongs in the physical category but when the body and adrenal glands are being used in this way it is using more of the physical components within the body of the medium than the mental.
For usual communication with the spirit world the adrenal glands are used but not as fully as they are for physical evidence. The guides use the brain, the pituitary gland, the thalamus and the hypothalamus for mental mediumship. The medium will sense this information often as pictures in the mind, or an urge to speak. They will give information to the sitter that they could not possibly know. This type of communication is usually quite smooth but the main stumbling block is the medium's own thought process. It is habit and human nature to try to work things out that don't make sense. We have to understand puzzles and the human brain is programmed to solve problems. In order to be a good medium it is necessary for the medium to hand over the use of their brain to the guides, therefore being passive and quieting their own mind. The medium is the bearer of the message, the middle person and should never change or influence the content of the message although sadly this does happen. Either through lack of development and training, lack of understanding or sometimes the medium just keeps talking and passing information to a sitter in order not to appear incapable. These readings are usually meaningless to the sitter and a good medium will tell the sitter that they are not getting anything for them, you can't force mediumship. If you are seeking a medium always ask what training they have had and if they belong to a recognised governing body.
It is true that a medium will sense and feel all that a spirit wishes to convey via the guides and also true that sometimes the symptoms stay with the medium for a while afterwards as the energy takes some time to dissipate from the nervous system. A trance medium suffers greatly for their service. After just a twenty minute trance session a medium will need five days to a week to recover, every muscle hurts, there is a soreness in the body similar to that felt when you get the flu, the fatigue is great and the brain fogged. The wear and tear on the body is huge, but many trance mediums feel it is worth it for the results of spirit evidence. I have witnessed transfiguration and it is an amazing thing to see demonstrated but it is rare because it takes a certain kind of person to be able to give themselves over to spirit completely. If you get the chance to see it - take the opportunity to see the rare phenomenon.
It's very difficult for a medium to hand over control to spirit, the human spirit is programmed to stay in the heart chakra until the point of death, so to leave before that time is unnatural. The medium has to force their body and mind into a relaxed state and push their consciousness from their body to a place of rest while the body is used by spirit beings. The medium's spirit has a strong desire to re-enter its bodily vehicle so many hours of practise are needed to maintain the trance state for any length of time.
When the trance state begins the medium is often in a sitting position, they may feel tipped in any direction, they may spin and feel pulled from their body. A cobweb sensation can be felt over the face and numbness of limbs and extreme cold may or may not occur. The ears buzz and ring and there is deafness and the eyes often burn. Nausea is felt and at the last second a burst of fear. It is hard to relax in such conditions but there are trance mediums whose dedication brings clear evidence time and time again.