I don't intend to be offensive by this but don't get too caught up in figuring out which category a medication is in, such as anti-depressant, mood-stabilizer, anti-psychotic, anti-seizure, anti-anxiety, hypnotic, and so forth. These boundaries are abstract and many medications fit into several categories because their effects can be more wide-spread than their category name suggests. For example, several anti-seizure medications are also effective anti-psychotic and hypnotic medications, whereas many anti-psychotic medications are also effective mood-stabilizer, anti-anxiety and hypnotic medications.

Back on topic, although Paxil and Trazodone are both anti-depressants, they have many differences, starting with the type of anti-depressant. Paxil is a SSRI, the type of anti-depressant you often hear and read about as being very effective. Trazodone is a SARI, which acts upon the serotonin system (as do SSRIs) but in a different way. The details aren't important, although if you want I'll explain some of them later. Some of the key details are mentioned below.

A fundamental difference between Paxil and Trazodone is Paxil is an effective anti-depressant. It has a much stronger binding affinity to certain serotonin receptors (5-HT2C) as well as to a mechanism called the serotonin transporter (SERT). On the other hand, Trazodone has a very weak binding affinity to SERT and serotonin receptors.

Trazodone has a stronger binding affinity for alpha-1 (α1) adrenergic receptor. While it also has a strong affinity for serotonin receptors, it targets 5-HT2A instead of 5-HT2C like Paxil. The combination of targeting 5-HT2A and alpha-1 adrenergic receptor lead to moderately strong sedation effects. In other words, it's more of a hypnotic than an anti-depressant.