sir call me crazy..but the exact same thing happened with me yesterday...with my Honda CITY 2005 model... my right headlamp bulb gave out 
i also had changed them to narva's H4 bulbs.... a week before from yesterday my DIPPER(High Beam Switch) got faulty..meaning it would not stay on the high beam for more than 3 mins or so..would jump back to low beam..i mean got kinda loose...
now that u guys are talking about this im feeling that this switch problem also happened cause of the narva's...or not ?
so to sum it up my RIGHT HEADLAMP ALSO GAVE OUT....and a week before that the high beam switch fault...what do u guys reckon....
one thing to note that when installing the headlamps...the guy said "ke aapki Grip loose hai" filhaal chal hi jaye gi but just letting u know...
was it because of that...
also lemme tell u the ratings of the stock City 05 bulbs and the Narva H4's..
Stock City bulb: it has some OSRAM bulb 12v 60/55W
Narva H4: 12v 100/90W
so what do u guys reckon... pls note that i do have an aftermarket audio system in the car too... around 800-1000W RMS...but i have grounds upgraded to 0 Guage wire...
also my wiring is not damaged..just that GRIP thing that the installer mentioned...would that have caused it ?
also my headlights dont dim much if at all when the bass hits..just so ya know...