A synopsis

It affects blood pressure.  In fact, certain stimuli can cause momentary flushing.  Hormones in the mind are affected and increased in some manners.  Pulse rates vary, in some cases individual heartbeats are affected and sometimes even skipped.  Nausea and anxiety are common.  Although not physically, the symptoms can be spread or even sought with prolonged exposure to another with them through a mental process.  Curiously, unpleasant side-effects can become even more severe after the stimuli are removed, showing signs of withdrawal.
Based on this evidence, romantic love is either a disease or a drug.   Curious