There are a lot many causes of groin pain,
Here is a list of some of them...
1) Muscular:
Rectus femoris, Psoas, Rectus abdominus,
Sartorius, Adductor longus, Pectineus,
Tensor fascia latae
2) Skeletal:
Femoral neck/ shaft fracture, pubic bone,
joints (hip joint, sacro-iliac, pubissymphisis,
lumbar spine)
3) Other soft tissues:
Joint capsule, bursa, ilio-femoral ligament,
nerves, blood vessels, lymph nodes,
hernias, genitalia (ovary, testicle etc.)
4) Previous medical conditions:
Perthes disease, slipped epiphysis.
The problem needs to be assessed by a clinician / possibly orthopedician for the actual causation.
The good news is that most of these causes are not life threatening...
The fact that the pain has improved/ disappeared indicates that possibly the cause was transient and possibly related to a soft tissue/ muscular problem.
I would advise an ortho opinion if the problem recurs,
All the best,
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Regards
Dr. Gupta