‘Sleep’ is frequently used in the NT to allude to death.
1 Corinthians 15:50-52New American Standard Bible (NASB)
The Mystery of Resurrection
50 Now I say this, brethren, that flesh and blood cannot inherit the kingdom of God; nor does the perishable inherit the imperishable. 51 Behold, I tell you a mystery; we will not all sleep, but we will all be changed, 52 in a moment, in the twinkling of an eye, at the last trumpet; for the trumpet will sound, and the dead will be raised imperishable, and we will be changed.
Jesu stated clearly: “Then said Jesus unto them plainly, Lazarus is dead.”
John 11:14.
No question Lazurus was dead.
He was in the tomb for four days. He was all wrapped up in burial clothes.
When he was called back by Christ, the Bible did not feel the need to tell of his experiences.