What is the real difference between solitude and loneliness if not a spiritual matter?

Cutting to the chase, I sometimes find myself alone and enjoying the simple peace and independence that such time allows: reading, writing, listening to music, or riding the currents of thoughts and dreams. This is a type of alone time I truly cherish - I think of this when I use the word solitude.

Then there are times when I'm uncomfortably alone. Times when my thoughts and emotions run chaotic and intense, times when tumultuous tides seem to push me about from one feeling to another - and my natural reaction is to try to change the way I feel from the outside. These are dangerous times. Strangely enough, I am as likely to have these moments of loneliness when I am in a crowd of people as when I am alone. Loneliness seems to come from internal unmet needs, a sense - real or perceived - of lack, of want.

There are also moments when, as I live my life and learn the patterns of relationships and inward realities - that my loneliness will turn to solitude.

Recently, I came across this song by Suzanne Vega that captures part of this experience beautifully. I do like her poetic lyrics.