No, You Do Not Need to Worry About Concussion or Brain Bleed
Based on your description of a very low-speed collision (few mph) with no direct head impact and zero visible car damage, you are at negligible risk for concussion or intracranial bleeding and do not need medical evaluation.
Why You Can Be Reassured
Mechanism of Injury Does Not Meet Criteria
The 2023 ACEP Clinical Policy 1 and ACR Appropriateness Criteria 2 define mild traumatic brain injury (mTBI) as requiring "mechanical energy to the head from external physical forces" with specific clinical features:
- Loss of consciousness (even briefly)
- Confusion or disorientation
- Post-traumatic amnesia
- Focal neurologic deficits
- Headache, vomiting, or other neurologic symptoms
You have none of these features. You did not hit your head on anything, experienced no loss of consciousness, and have no symptoms.
The Physics Don't Support Brain Injury
Research on rear-end collisions demonstrates that even at speeds significantly higher than yours, the risk of concussion is negligible. A 2018 study 3 examining rear-impact collisions at 15.5 km/h (9.6 mph)—more than triple your speed—found head acceleration values "far below published automotive injury risk values" with "negligible risk of concussion." Your collision at "a few mph" with the car merely bouncing would generate even lower forces.
The 2020 meta-analysis 4 examining concussion potential in motor vehicle collisions found that the change in velocity (delta-V) required to reach even theoretical concussion thresholds far exceeds what occurs in very low-speed parking lot impacts like yours.
When You WOULD Need Evaluation
According to ACEP guidelines 2, you would need a CT scan only if you had:
- Any loss of consciousness or post-traumatic amnesia PLUS one of: headache, vomiting, age >60, short-term memory deficits, physical trauma above the clavicle, seizure, Glasgow Coma Scale <15, focal neurologic deficit, or coagulopathy
- Without loss of consciousness: focal neurologic deficit, vomiting, severe headache, age ≥65, signs of basilar skull fracture, Glasgow Coma Scale <15, coagulopathy, or dangerous mechanism (ejection from vehicle, pedestrian struck, fall >3 feet)
Critical Caveat About Anticoagulation
The one exception where you might need evaluation despite minimal mechanism: if you take anticoagulants (warfarin, NOACs like apixaban/rivaroxaban) or antiplatelet agents (clopidogrel, ticagrelor—but NOT aspirin alone) 1. These medications increase risk of delayed intracranial hemorrhage even after minor trauma. However, even in these cases, the trauma must involve actual head impact, which you did not have.
Bottom Line
Your scenario—very low speed, no head contact, no symptoms, no visible damage—does not meet any threshold for traumatic brain injury evaluation. The forces involved were insufficient to cause brain injury. No medical evaluation is needed unless you develop new symptoms (severe headache, vomiting, confusion, vision changes, weakness, or altered consciousness).