The psalmist describes the ever-increasing emotions that he is having because of the problems in his life, and the anxieties and pressures and depressions that were building up inside him.
The problems are not described, because there are many problems in the world, and this inner pressure can apply to anyone.
The term musing, describes the pondering or the meditation or the mental thinking activity that was going on in the mind, because of the problems.
The psalmist watches carefully over what he says, in the presence of others, fearing that he might blurt out something, perhaps even blaming God, and that would have a native impact on how others might perceive God.
The fire burned within, describes the ongoing and ever-increasing agitation within his mind, such that he reached the boiling point and was no longer able to remain quiet.
And so he speaks.
And the remainder the Psalm describes the words that are spoken, as he vented his pent-up feelings. And even though there was a feeling of murmuring and complaining, the psalmist seeks relief in stating his difficulties before God, but at same time seeking from God, direction and support.
