The impact of software vulnerabilities on everyday software systems is concerning. Although deep learning-based models have been proposed for vulnerability detection, their reliability remains a significant concern. While prior evaluation of such models reports impressive recall/F1 scores of up to 99%, we find that these models underperform in practical scenarios, particularly when evaluated on the entire codebases rather than only the fixing commit. In this paper, we introduce a comprehensive dataset (Real-Vul) designed to accurately represent real-world scenarios for evaluating vulnerability detection models. We evaluate DeepWukong, LineVul, ReVeal, and IVDetect vulnerability detection approaches and observe a surprisingly significant drop in performance, with precision declining by up to 95 percentage points and F1 scores dropping by up to 91 percentage points. A closer inspection reveals a substantial overlap in the embeddings generated by the models for vulnerable and uncertain samples (non-vulnerable or vulnerability not reported yet), which likely explains why we observe such a large increase in the quantity and rate of false positives. Additionally, we observe fluctuations in model performance based on vulnerability characteristics (e.g., vulnerability types and severity). For example, the studied models achieve 26 percentage points better F1 scores when vulnerabilities are related to information leaks or code injection rather than when vulnerabilities are related to path resolution or predictable return values. Our results highlight the substantial performance gap that still needs to be bridged before deep learning-based vulnerability detection is ready for deployment in practical settings. We dive deeper into why models underperform in realistic settings and our investigation revealed overfitting as a key issue. We address this by introducing an augmentation technique, potentially improving performance by up to 30%. We contribute (a) an approach to creating a dataset that future research can use to improve the practicality of model evaluation; (b)Real-Vul– a comprehensive dataset that adheres to this approach; and (c) empirical evidence that the deep learning-based models struggle to perform in a real-world setting.