Subset data in R on the condition of decreasing values

couldn´t find a question alike, so here we go: I have a large dataset in R and I want to prepare it for hazard analysis. I thus want to create a dichotomous survival variable. However my hazard event has a relative interpretation and is not just a certain value being 0. The dataset is of the form:

ID    y
1     0
1     15
1     30
1     29
1     10
2     11
2     64
2     86
2     79
2     75

plus a bunch of independent and control variables. The IDs enter the subset fit for survival analysis as y > 0. Back to the hazard variable: I want it to take on "1", as decreasing values of y fall below a threshold, which is 75% of the highest value y reaches with respect to the ID groups. Thus two conditions have to be fulfilled for the hazard:

1. the values fall below the threshold (with respect to their IDs)
2. the values are decreasing. So if there is a y column like the one above, for the first two values of ID 2 the hazard variable should not be coded "1", as the values might fall below the threshold but are higher than the previous value.

Anyone got a solution for that? Thanks in advance?