I've been feeling really sad but can't cry. i want to let it all out so this knot in my throat and tightness in chest go away but it's not happening. is this some sort of condition?

Too sad to cry: Have you heard the song numb? By usher i think about this. Like it is too cold to snow it is too sad to cry. Cry can happen only when your heart is open. Heart if hurt too much shuts off. Once you heal the numbness later it will be safer to cry. In some situations I use prayer shawls. Use a blanket or shawl and bring this to your prayer place and use this until you heal like kids safety blanket.