It all depends on the aircraft type and knowing your POH.
Its well worth reviewing the POH (before flight) so you know how much of a problem an unlatched door might be.
On many types it is non critical and no cause for alarm.
On some it is an emergency - you dont want the door to unlatch on an Aztec for example.
To be harsh, if its non critical you may have been unnecessarily alarmed which caused the height loss, whereas had you known it was not critical you could have taken time to deal with the issue. Alternatively as is some times the case the first action may have been to slow down, whereas by reacting to the emergency in terms of an anxiety to latch the door you might have ended up speeding up and achieving exactly the opposite result.
Never the less well done you sorted out the problem and all is well.