How many chapters is this exactly?

[Very Good, Very Evil]

I'm looking at the achievements and i see that it lists 1-13 and complete the game all next to each other but then way down the list I see 17/18 yet nothing for 14/15/16. Are those missions just incredibly short or are 17/18 related to the DLC?

Also, I just completed the medical bay part (chapter 5) which gave me some major heart palpitations! Without spoiling anything, are there any parts that even match the tension found in that area later on?

[Swans]

I believe it is 18 chapters in the game campaign.

[Clarktronics]

There are lots and lots of bits to match the tension of the Medical Bay.

[Swans]

Agreed. I found the tension pretty much unrelenting. I play this game in 'short controlled bursts'. It's the only way to be sure.

[Very Good, Very Evil]

Yeah, the tension is getting to me. I was able to get through Amensia and Outlast without even flinching but this...this one is getting to me. Then again, something about deep space gets to me. I was the same way with Dead Space.