There's a dent in the middle of my fingernail, it almost looks like it collapsed, its the best I could describe it. What could this be?

Trauma vs inflam'n. Indentation in the nail plate is generally caused by injury to the nail matrix, which sits under the skin where the nail grows out (opposite end to the free edge of the nail called proximal nail fold). So, either trauma (ie from picking) or inflammation (ie chronic eczema, or psoriasis) can cause nail plate abnormality. To avoid permanent scarring, see your dermatologist for evaluation.
Nail dystrophy. Based on your description it may be a type of nail dystrophy known as central nail canal-like or median nail dystrophy. This usually results from trauma to the nail (usually nervous habit of rubbing the proximal nail/nail fold). Best thing to do is to have it checked.