I was guilty of the 'seven iron only' on the driving range. Now I practice as I would play a bogey par 5 starting with driver then 3 wood, 6 iron, 52 or 56 wedge then finish with a chip, pitch or lob shot at 10-15 yards or so.
You've either brought something into or omitted something from your usual swing that has had a negative impact. Could be something as simple as timing. This is usually the case of high handicappers though who haven't an ingrained swing.