Possible Clues:

• Depression: it is a medical condition
• Intestinal disease
• It's a firm fifty, so it is, with trouble inside
• It's a pass, so it is, to cause trouble inside
• Intestinal inflammation
• There's trouble inside for 17 across, so it is
• There's trouble inside for the way over the mountains, so it is
• It's a pass, so it is, that will give trouble inside