BUG / Question: Cant loop over Full/Complete DataFrame Index
I have been looping over dataframes from selected indexes. Works fine for the most part, however, when trying to loop over the entire dataframe (rather than using .query() and then saving the queried index), I get KeyError: 4393 


Why I think this is a bug is because I can make it work by doing:
```
dfDbi = dfD.head(4390)  # dataframe has 4393 keys, tried .copy() but no luck with the for loop
dfDbi = dfDbi.query('OC<0').index #saving index to later loop through

# pseudocode
for x in dfDbi:
    if dfD.loc[x] and dfD.loc[x+1] condition true:
        (do something)
```

The above works. Changing dfD.head to (4391) or higher does not. 
What I want to do is:

```
dfDi = dfD.index 

for x in dfDi:
    if dfD[x] and dfD.loc[x+1] condition true:
        (do something)
```

If I have butchered my explanation, please let me know so I can try to further explain.