join table with itself?

I am not getting to grips with the following query:

set-up: Postgresql 8.1

The table HISTORY contains stockmarket data:
DAY        HIGH    LOW        
2007/02/28    6286.1    6166.2    
2007/02/27    6434.7    6270.5
2007/02/26    6446.8    6401.5

I'd like to produce the following result:
DAY        HIGH    LOW    DAYS2FALL    HIGHEST
where DAYS2FALL is the number of days it takes for LOW to fall below the 
present row's LOW
where HIGHEST is the highest HIGH during that period.


I had a stab at DAYS2FALL:

SELECT  present.day, present.low, (MIN(future.day)-present.day) as 
days2fall FROM history AS present,history AS future
WHERE    present.day < future.day AND    future.low <= present.low
GROUP BY present.day,present.low
ORDER BY days2fall DESC

but didn't manage to express HIGHEST. Also, my attempt isn't exactly the 
fastest.
-- 


Regards,

Tarlika Elisabeth Schmitz