Either I saw him or I didn't and I'm crazy for real this time, she thought. (1.1)
This is the first line of the book. It's tricky because it tells you Connie might be crazy, but you don't really know what she's talking about, so you don't see her as mentally ill through that first chapter when she smashes Geraldo in the face. Does it change your reading of that chapter when you know that she may not be in her right mind? Should it?
"I went mad with fear. In the madhouse I met Bolivar and he was good for me in learning to say the initial 'I want. I want.'" (6.131)
Jackrabbit ends up in the madhouse because he has trouble deciding what he wants, and he gets afraid as a result. That makes madness seem like an everyday problem; something you and your neighbor and your Uncle Bob might experience, rather than something that only happens to messed up people like Connie.
"Do you tell everyone you meet that you've been mad twice?" (6.152)
Connie is envious. One of the worst parts of ending up in the asylum for her was being stigmatized; everyone thinks she's a horrible person because she was committed. It's hard to get better and live a normal life when the world thinks you're awful.
"Most we've reached are females, and many of those in mental hospitals and prisons. We find people whose minds open for an instant, but at the first real contact, they shrink in terror." (10.45)
Luciente says that many of the people they contact from the future are in mental hospitals and prisons. The suggestion is that receptive people like Connie are often mistaken for being crazy in the present. It also means that people who are seen as marginal and wrong and broken are actually the good guys.
Dizzy, she stuck out her hand, and Dolly again gave her a five. Oh, well, she could use it. She stared into Dolly's intense eyes, the pupils too big, too shiny. "What are you on?" (11.25)
Connie's in the asylum, but Dolly is the one so confused and messed up that she literally can't even remember what she's doing from one minute to the next. The difference is that Connie fought back when Dolly was in danger, and Dolly didn't. Which makes it look like the asylum is meant to control and pacify, rather than to heal.
As soon as the orderly left she climbed down. (11.171)
Connie has made herself unconscious in order to escape. Luciente taught her how to do that… which means Luciente must exist, right? This is the moment where it seems Connie is most likely not crazy. (Though of course, we learn everything from Connie's point of view, so maybe she's misleading us?)
A voice in her ears, good-natured, chiding: Luciente as a fraction of her mind, as a voice of an alternate self, talking to her in the night. Perhaps she was mad. (12.126)
As the book goes along, Luciente often seems more like a voice than a real person—and here Connie explicitly wonders if Luciente is an alternate self or a kind of imaginary friend. But if Luciente is imaginary, how can she tell Connie which plants are safe to eat?
"They won something. I don't feel like f***ing anybody. Or loving anybody. I don't feel any love at all. I feel like a big block of ice." (14.113)
Skip's homosexuality is seen as an illness. Curing him involves making him unable to feel lust or love. They've cut out a bit of his brain, which seems like it leaves him more insane, not less. (This is confirmed when he finally succeeds in his suicide attempt.)
… she could pour some of the poison into the coffee. It was brown and oily. It would work well in coffee. For all the meanness he had laid on her all the years of her life, for Dolly, for Carmel. Her purse lay within reach. She could do it. (18.178)
Is Connie mentally ill when she contemplates killing Luis? Is it rational to want to kill him? If she did murder him, she could probably escape the house in the confusion, or at least make an attempt. You could see her violence as extreme or crazy, but she's in a pretty desperate situation; maybe it's sane to go a little insane when you're backed against the wall.
She thought of Luciente, but she could no longer reach over. She could no longer catch. She had annealed her mind and she was not a receptive woman. She had hardened. But she thought of Mattapoisett. (19.109)
Connie can't reach Luciente at the end of the book. You could see that as meaning she's become sane. But the description makes it sound more like she's insane. Like Skip, she's cut herself off from others, which is a kind of death and a kind of insanity.