Hearing music while meditating

I had something rather peculiar happen last night. During meditation it's normal for me (and most) to hear slight ringing in their ears. So last night while meditating, this ringing 'sound' began changing frequencies. It turned into multiple high frequency 'tones' (best I can describe them). Initially they were dissonant but after about 30 seconds became very harmonic. It was like a symphony of these vibrational sounds. It was very pleasant and I did not want it to cease.

Also, while this was happening, it felt as if a vibration was going through my head. Imagine putting two tuning forks against your head - each on the opposite side.

Anyone had similar experiences??? And what could this be? Am I just losing it?