Truly, Madly, Deeply: How Love Makes you Sick Cupid's bow can kill your appetite, nuke your focus and interrupt your sleep. By Jennifer Nelson TODAY.com contributor Rae Padilla Francoeur, 63, of Rockport, Maine, has been in plenty of passionate relationships before but when she met her current mate, she fell head over heels. Who'd have thought it would take a terrible toll on her health? Francoeur, the author of "Free Fall: A Late-in-Life Love Affair," says "the physical manifestations were extreme." During the lovesick phase she became lightheaded, lost weight, couldn't sleep for days, had butterflies and a quickened heart rate and couldn't concentrate or eat. "I was happier than ever emotionally, even though I couldn't eat and felt shaky all the time," says Francoeur who also ended up with a year's prescription for a prophylactic antibiotic for chronic urinary tract infections, too. Scientists have since learned that a chemical cocktail of neurotransmitters - phenethylamine, dopamine, norepinephrine and oxytocin - are at work when we fall for someone. This powerful love potion is secreted when we feel that initial attraction and serves as an amphetamine, elevating our mood, keeping senses on high alert, and helping us bond with another person. "Falling in love affects your brain about the same way as smoking crack," says Ethlie Ann Vare, author of "Love Addict: Sex, Romance, and Other Dangerous Drugs. "It has essentially the same effect on what's called the reward center of the brain." Once smitten, these "love" chemicals surge and their health effects are set in motion. Some people, like Francoeur, are particularly hard-hit. Here's a few of love's side effects. They don't call it lovesick for nothing. Can't sleep Having a hard time sleeping is a direct result of too much dopamine and norepinephrine. "You're on a speed high," says Dr. Helen Fisher, author of "Why Him, Why Her?" and a leading love researcher at Rutgers University. "This is why you have so much energy, why your face is flushed, and why you can walk till dawn and make love around the clock." Francoeur says the first time she and her beloved were together they didn't sleep for three nights. She then put in ten hour days at work. "I literally burnt the candle at both ends for two years." Can't eat Francoeur describes having lunch with a friend while lovestruck saying "she's ordering everything on the menu and I can't even swallow." Psychologist Dorothy Tennov coined the term "limerence" to explain this crazy phase of infatuation. Limerence is the obsessive, intrusive, and all-consuming state we're in where we justify letting work, friends, responsibilities - even ourselves - slide so we can satisfy our unquenchable thirst for our new partner. Friends questioned Francoeur's weight loss - about 15 pounds - but she was apathetic to do anything about it. Thankfully, studies show these intense feelings only last somewhere between six months to two years. Advertise | AdChoices Can't concentrate You may think very clearly, but you can't think about anything but him or her. It's the dopamine that gives you that obsessive focus. Romantic love is an obsession. You can't stop thinking about the person. But you're thinking of every detail of them: what he said, how she moved, what he meant by that. You're focused - just not on work or your to-do list. Not surprisingly, some of us actually chase lovesickness. "Probably about 6 to 10 percent of the population is born with poorly functioning dopamine receptors," says Ware. To them, everything feels a little black and white blah until they are shot with cupid's arrow and get that reward cascade cocktail of neurotransmitters pumping. Then they think, "Wowsa! Life is in color!" And they continue to chase that feeling. Problem is, nature didn't expect for us to spend that long in the pursuit period. Nature expects us to settle down and procreate. Chest pressure When people feel chest pressure, it's probably panic, says Fisher. When you first fall in love brain circuitry is linked with panic and anxiety. Fisher and her colleagues scanned over 75 people's brains that were madly in love and found they showed activity in part of the insular cortex of the brain, which is linked with fear. Some scientists go so far to liken limerence to mental illness. People in a manic state, for example, show an abnormally heightened mood, self esteem, and sense of anxiety and tend to do out-of-the-norm things, like make rash decisions. Nausea and butterflies Most of us have had a queasy or nervous feeling in our stomachs just before something important is about to take place. Falling in love is equally important. Nature sure thinks so. Fisher explains the queasy stomach is the same feeling you might experience before a big exam, a job interview or stage fright. The release of norepinephrine, dopamine and cortisol divert blood away from the gut and give you that off your stomach feeling that signifies I'm so excited I might vomit." Lovestruck folks may also contend with sweaty palms, weak knees, dry mouth, increased heart rate and light headedness. The good news (if you don't break up): Limerence turns into a calming deeper attachment, and these health side effects subside. Romantic love evolved to focus our attention on someone special and start the mating process. And though that early jolt of passion and preoccupation may feel wonderful, it's just not sustainable, says Fisher. "Once you have that baby, you can't spend your time running around the dining room table chasing each other; otherwise who's going to take care of the baby?" © 2011 MSNBC Interactive.