How to fit a slope line after each peak?

Hi, I have 2 variables X, Y. Somehow Y is declining whenever X peaks. I am interested in looking at how Y recovers after each peak of X. What I did, is that I found all the peaks in X by findpeaks. I then determined the value of Y one day before the peak as my "Pre-peak" value. I need to determine how long does it take Y to recover to pre-peak value. How many time steps does it take for post-peak value to go back to pre-peak value. The common way this thing was done is by fitting a line to post-peak data that intersects with pre-storm data and get the slope of this line. Any idea how to do this please or any better way? I hope I did not confuse you.

[Carl]

Hi Karoline, can you provide more details on your data, and your current workflow?

1. Can you provide example data, or maybe an example plot of what your data looks like?
2. You stated that your current workflow involves fitting post-peak data with "pre-storm" data, and getting the slope. Can you explain the data being used to fit this line, and how you use this to calculate the Y recovery time?