One can see what will trouble This sleep of mine, whatever sleep it is.
The speaker is still predicting what kind of dreams he will have. He says that it should now be clear which images will haunt or "trouble" his sleep. In other words, images of apples, of falling, of ladders, and more.
The word "trouble" is unexpected, because it implies that these images are disturbing to him in some way. The poem invites you to consider why they might be disturbing, but it does not answer this question.
Finally, he expresses uncertainty about what kind of sleep he will have.
Were he not gone, The woodchuck could say whether it's like his Long sleep, as I describe its coming on, Or just some human sleep.
He wonders whether he will sleep like a normal person, or like a hibernating creature, such as a woodchuck.
He must be really tired from the harvest. You've probably had one of those days when you feel like you could sleep for three days straight. The speaker thinks he could sleep for three months straight.
A woodchuck is a groundhog, and we all know from a certain famous Bill Murray movie that groundhogs hibernate in the winter and then wake up on February 2nd – unless they are being cranky.
The woodchuck is an expert in hibernation, so it could say whether the speaker is about to go into hibernation. Unfortunately, the woodchuck has already gone to sleep for the winter, so the speaker will get no answer to his question.
He sounds like he would be disappointed with a "human sleep," even though we all know that's what he's going to get.
We can only assume that at this point the speaker does, in fact, go to sleep. Good night, buddy.