We can only speculate. I have heard many opinions, stories ect... There are enough confessed experiences and extrapolations to suggest:
1). non-existence
or, on the brighter side of non existence is the idea our bodies go back into the natural life cycle of the planet. (worm food)
2). eternal life; damnation and/or bliss
3). reincarnation
4). we are absorbed and become one with the universal consciousness and/or god
5). (insert personal belief here)
As to physical sensations, I have seen death and it's not pretty. I don't believe there is any passing through the curtain of death that is without physical, emotional and spiritual trauma. And for what?! We don't really know for sure. Could be 100 times worse or peace or nothing.
Personally, I'm inclined to think it was set up, (designed if you will) that we never know the truth this side of death, but to what end I do not know. Perhaps to ensure survival, complete a purpose or learn wisdom, patience and endurance so as to better our soul.
Either way, Life is a precious comodity. Our circumstances may be bleak, our will sapped, energy low, self esteem low, helplessness, hopelessness and pain... but our life is a light to others. This is always experienced when someone we know dies. It is like a light has been snuffed out and our world gets darker. Perhaps the closer you are to someone the stronger their light is for you. But there is always a knowledge of loss. And no light is independant of others, no matter how well we have withdrawn and pulled away from others. You are someones light.
Depression darkens our persepctive. We can fail to see our own light and the light of others. We can believe they don't care or we do not care. It is a terrible illness with a terrible price because of the emotional loneliness, isolation, emptiness, .. hopelessness.
But I would like to take this moment to remind you that your life is precious. That you are part of this world and a light to others even though you see darkness. That there is hope even when we can't see it. I can't see Dallas Texas from my home here in North Dakota. But I know it's there, and if I drive and drive and persevere it will rise up over the horizon eventually.
Our hope and health is like that. In this darkness we have to strive to make intentional choices for our well being; forgive, love and accept ourselves. Seek help and support from others. Plant the seed of hope. Water, fertilizer and protection will, in time, yield results. And when someone steps on the tender roots or chops it down ... as long as there is life there are seeds.