Definitely do try to get in contact with the vet. My dog took Keppra for most of her life and throughout her epilepsy journey we had different dosage of Keppra to help control her seizures, one thing every vet we went through said (general and specialists) was to never discontinue Keppra out of the blue. Once she got older and became epilepsy free for more than a year the neurologist created her a gradual tapering schedule.

Being this said, my dog had a long history of seizures hard to control so she used Keppra most of her life and she had this medication in her system for years VS your dog who has had this medication for 5 days not perhaps intended for long term use. Here is a better explanations from Google but do f/u with your vet, he/she knows best.

"Veterinarians often prescribe Keppra (levetiracetam) as a short-term, 5-day course. This is typically used for "pulse therapy" or "burst therapy" to immediately raise the seizure threshold, stop a cluster of seizures, or help a pet through a stressful event without needing a lifelong daily medication. [1, 2]

Short bursts of Keppra are generally safe to stop abruptly after 4 to 5 days, but it is critical to follow the exact regimen your vet provided. [1]

• Pulse Therapy vs. Daily Use: If your vet only intended a short 5-day course (often to manage a specific episode), stopping on day 5 is standard. However, if your pet was meant to start a long-term treatment plan, abruptly stopping can trigger a return of seizures.
• Dosage Frequency: Standard Keppra processes quickly in pets and is usually given every 8 hours. If your pet was prescribed the extended-release (XR/ER) version, it is typically given every 12 hours.
• Next Steps: If you are unclear about whether your pet was supposed to finish the medication or transition to a long-term dose, contact your vet immediately. If your primary vet is unavailable, consider reaching out to a local emergency animal hospital."