While-loop over dataframe running forever

Many apologies for the inane question, but I just can't seem to figure out why one section of my code won't display an output, and runs seemingly indefinitely. Hopefully it is immediately obvious to someone here, and then I can bang my head against my desk at how obvious it was.

Here is the snippet:

i = 0
j = 0

while i < len(data):
    if data['Pos'][i] == 1:
        while j < len(data[i+1:]):
            if data[i+1:]['Close'][j] >= data['High'][i] or data[i+1:]['Close'][j] <= data['Low'][i]:
                print('The position that was opened on date', data.index[i],'was closed on date', data[i+1:].index[j])
        j += 1
    i += 1          

data is a pandas DataFrame with datetime index, and columns Pos, Close, High and Low.