You can alive walking and talking and be dead on the inside.
AND YOU [He made alive], when you were dead (slain) by [your] trespasses and sins
Eph 2:1.
This verse tells us that unbelievers are spiritually dead in their sins, awaiting a future judgment. This "spiritual death" does not imply they are literally dead or non-existent but rather separated from God's spiritual life due to their rejection of Christ.
Alive in Christ is the way to go.