MacBook Horizontal Lines Appear / Disappeared - Display Issue

Hi everyone, I’d appreciate any, and I’ve provided some pictures as well for reference.

To start, I got this MacBook 4 years ago and it really has been great throughout having it - until 1.5 months ago. I work remotely from home, so I use my computer daily on a desk. In early January, I was working when my screen had horizontal lines appear near the bottom. I don’t know if they had been there for the few hours I was working or had just appeared, but it was several thin, darker lines. 

After a quick Google search, I closed the Mac for the day in hopes it would not cause lasting issues. Cut to the next day, I opened my Mac only to have lines flutter across the ENTIRE screen after having it on for only a few minutes. I FREAKED out, as this had all come out of nowhere. 

The next weekend, I took a day trip to the closest Apple store where I was informed the display most likely was the issue and was given a ballpark price of $700 to send it off and have it (hopefully) fixed. I couldn’t afford that; my nonprofit position pays little and I’ve spent most savings on medical school applications. $700 would have destroyed my remaining savings, so I opted to wait and save up first. 

After returning home, I researched and found that many individuals with the same or similar model have had these issues. Though I want just as badly to access an Apple replacement program to fix this issue in our models, my question is different today.

This morning, I opened my computer up and, like normal, the horizontal lines made it difficult to see clearly - but it was manageable as it’s been the past 1.5 months. After a minute or so, the screen cleared out of nowhere. It flickered a few more times but, overall, it stayed clear (except the very bottom and slightly at top). WHY did this occur after 1.5 months of the same display? HOW do I maintain this clarity in my display and ensure it doesn’t resort back to the lines? Does this mean I may not need a replacement, or is this more likely to be temporary? I seriously don’t understand, as I have changed nothing in the past weeks, but I really would love to avoid this issue as ya girl is broke and will be even further broke when taking out overwhelming loans this fall. Truly, any and all help is appreciated.