Lines become "squgly" after reopening a document

[Raman5F85]

So i was working in photoshop and finished up a rough sketch of a an art project i was working on. I save the document as a psd and close down photoshop. Later when i reopen it the lines are for some reason very "squigly" and not as smooth as before. I was just wondering if this is a bug, or perhaps a setting i turned on by any accident? If so i would really apreciate if someone could help me resolve this problem (first picture is after reopening photoshop, first one is before closing photoshop, the lines are much smoother in the first one)