Originally Posted by Wancata
Letting an abscess come out on its own is fine, but it takes longer and can sometimes get infected.
An abscess is an infection. It does not get further infected.
You do not mention in your original post anything about swelling or bumps or anything anywhere on the lame leg so I will assume there is not any.
A good percentage of the time if you have a sudden acute lameness with no obvious signs of something else being wrong the issue is an abscess.
Abscesses can seem to come and go. Basically two things could be happening. The abscess drained and came back (new abscess or if a foreign body caused the abscess the foreign body might still be there and be causing a new abscess). Or the abscess might be located such that the pressure tends to come and go.
Soaking in hot/warm water and Epsom salts will not hurt anything.
I would not recommend using hoof testers if you do not know how to use them.