I've got the feeling!

"In the 2013 science-fiction thriller Gravity, Sandra Bullock plays an astronaut who gets stranded in a capsule in space following a catastrophe in which she is the apparent lone survivor.

                                                                                                                                         
Cold, frightened, and alone, she resigns herself to her fate and shuts down the cabin's oxygen supply to commit suicide. As she begins to lose consciousness, she is visited (or is she?) by her fellow astronaut, played by George Clooney, whom she believed to be dead. He gives her a pep talk and a survival plan—and then he leaves.
                              

She eventually realizes that Clooney’s visit did not really happen, but the experience still gives her the strength to continue on. By following "his" plan, she is able to survive what seemed to be a hopeless situation. 

The movie was science fiction, but the encounter that Bullock’s character has with a "being" who appears in a moment of desperation is a human experience far more common than you might think. Psychologists refer to it as the “sensed presence.”                                                 (Frank McAndrew - Out of the Ooze)

This sensed presence scenario is quite common - most of us have had it. We feel that we are being watched or that someone is in a room with us, yet we just cannot see them. It may not be as dramatic as when we are at death's door ( although many sensed presences do occur at that time) but it can often happen when we are in an unusual environment, often when high levels of stress are involved.  

Mc Andrew goes on to say that, "the vividness of the presence can range from a vague feeling of being watched to a clearly perceived, seemingly flesh-and-blood entity such as Clooney’s character in Gravity. This entity might be a god, a spirit, an ancestor, or someone personally known to the observer. Sensed presences usually appear in environments with little variation in physical and social stimulation; low temperature is also a common ingredient."

There a a number of different explanations for this sensed presence scenario.

Is it environmental?
It has been said that high EMF exposure can make people hallucinate and have a sensed presence episode.

Stress?
Panic, high stress can create a change in brain chemistry - is it a way for the subconscious to get information through to us and past our panicked conscious mind?

Stimulation of the "God" part of the brain?

The sensed presence experience was a common effect in Dr. Michael Persinger’s lab in his so-called “God Helmet” experiments.

Researchers have been doing experiments that may suggest that there is a particular part of the brain that, when stimulated, leads the subject to believe that they are being haunted, seeing an apparition or being visited by angels or God.

Those also locked away and in an isolated environment with little outside stimulus also experience this hallucinatory state.

With nothing to focus on the brain goes within to find stimulation. 
Certainly we have all read or heard of people going quite mad in situations of sensory deprivation for long periods of time.
There is a lot of sense in the saying 'idol hands are the devil's play things'

Grieving individuals who have lost a loved one on whom they depended greatly may shut themselves off from social contact with others and rarely leave their homes.
This loneliness and isolation, coupled with high levels of stress and unchanging sensory stimulation, might very well produce the same biological conditions that could trigger a “visit” from their recently departed.

Some people will also have a sensed presence episode after long periods of meditation or introspective isolation where they may take themselves away to 'think about the future' or take part in a vision quest or a weekend retreat where, again, a lot of external stimulation is taken away and they are turned inward to focus on themselves.
Many religious types of visitations can occur in such a scenario.

So looking at these examples - when is a visit something external and when is it coming from within ourselves?

Is it our deep desire to see our loved one again the trigger that brings them through?
Do they come through or are we projecting it?

I have heard from many who never hear from anyone close that has passed.
That doesn't mean that they care any less - but why then do some people have a visitation yet others do not ( placed under the same pressure).

Is it a stressful situation what brings on a visitation?
Maybe seeing an accident, or losing your job or being in a financial bind triggers the mind the create a salvation scenario?
Or does our spirit guide truly come through to us at this point?

Maybe your next meditation will switch you on?
As you sit and let you mind be free - what will it conjure up?

Each experience is deeply personal and often healing and therefore who are we to judge.

We have all learned that in the world of paranormal experiences there is nothing that is 'normal'.

Maybe the next time you have that 'feeling' check out where you are, what you have recently been through personally, how are you emotionally and physically, what about the environment you are in when it happens?
Are you the only one present when the visitation happen?
How often has it happened to you?
The questions are endless and that's what makes it all so fascinating.