Deneen,
As far as a surge of energy, I guess that would describe what my daughter had. But it was at the very end, literally in her last couple minutes of life. There was no prior indication that this would happen. So I don't think there is any way you could know if and when it might happen. It also may not be as much as you expect. For what it's worth, here is what happened.
Like your friend, Heather also couldn't talk. Plus she had a spinal tumor which had left her paralyzed. All she could move in the last several days of her life was her head, actually only her eyes in the last day or two. In the last moments of her life, though, somehow she came up with the strength to squeeze my hand a few times. This action was in response to the hospice nurse talking to her. Heather was heavily sedated when the nurse noticed the signs of impending death, a change in her breathing, etc. So she was telling Heather in a clear, somewhat loud voice that it was alright for her to let go if she was ready. We told her that she didn't have to worry about her daughter, that she would be taken care of. And that we loved her and would miss her, but we knew she needed to go so she could be free of pain. I think squeezing my hand was her way to let us know that she heard and understood us. To be able to move those muscles, Heather had to have had a tremendous surge of energy. This of course is only one experience and there is no way to know what, if anything, your friend will experience.
I have been told that hearing is the last sense to shut down. The nurse said that even while sedated and seemingly asleep, sometimes a person can still hear. That is why when she talked to Heather, it was in a loud, clear voice. I would suggest that you go ahead and say your goodbyes to your friend in the same manner. Even if he doesn't respond, he still may be able to hear you. Just holding his hand and telling him how much his friendship has meant to you would be soothing not only to him, but to you as well. Touch can be very powerful. I hope this has helped to answer your question a little. I am just so sorry you all have to go through this. You have my sympathy.
Rainbows & hugs,
Rosie
