He--- doesn't know what it is but he feels something inside.
In his heart. Has this man got the flu?  
Or is he drunk? Well, the symptoms are similar. It was like this;

When he looks at her his heart runs fast and he gets warm even if the heating is off, he has hallucinations, he sings and laughs, he gazes at one point and smiles, he hears music wherever he goes, the light is on and off depends on

her presence and absence!   There are three things that we cannot hide.  
The first one is coughing. The second one is poverty. And the third one is 'LOVE'  
Yes, he is in love!  This mysterious thing called love bothers him
day and night and night and day!