Sometimes you think you’re in love, but let me tell you something, you are not, there’s no such thing, you have to check yourself because you may have a medical problem. just see the list below.
when you can’t stop thinking about him/her it’s not love, it’s maybe Obsessive–compulsive disorder, or OCD. try having “Paroxetine” everyday, and and you may get better.
And sometimes you have that restless trembling of body parts, like hands and feet, or some other parts, you’ll think it’s love, but it’s not, it’s maybe Parkinson's Disease, in that case try some “Stalevo” and you may get better. 
A Skippy heartbeat or heart rate that exceeds the normal range when you think of him/her, is not love. it’s maybe Tachycardia, which may lead to ventricular fibrillation and myocardial infarction (heart attack). I advise you to seek immediate doctor attention, and to have an 12 lead electrocardiogram test.
Constant smiling is not because you’re falling in love, not even close to that. it’s maybe Bell's palsy, Treatment of Bell's palsy is a matter of controversy, all I can say is, Good luck with that.
if you have Insomnia, and you’re always thinking about him/her. it’s just not love, it’s maybe you’re having Hormone shifts, or Disturbances of the circadian rhythm, try having some “Benzodiazepines” and you may get better.
the feeling of him/her present when they are not around you, Feeling that you can smell/hear/feel him or her when not in his/her presence, is not love, it’s just a psychotic illness, Schizophrenia, try some atypical antipsychotic medication such as Risperdal, and seek immediate medical attention.
And if you have Absent mindedness, forgetfulness, inability to focus on tasks at work or home, it’s not love, it’s just maybe Alzheimer's Disease, if you’re old. and there’s no treatment.
A Frequent sexual arousal while thinking bout him/her does not mean you’re in love with that person. it’s just maybe Hypersexuality, or Nymphomania, though Nymphomania is not listed as disorders in the DSM-IV. I advise you of medical attention.